Enrichment for Grade-school Kids

google "Free museum days San Francisco" to find out which museums offer free admission on certain days of the month (If I remember correctly, SFMOMA and the DeYoung have free admission on the first tuesday of the month). The SFMOMA web site also has a great interactive called "The Country Dog Gentlemen Travel to Extraordinary Worlds" http://countrydogs.sfmoma.org/ - in which the two painted canines serve as "tour guides" through a couple of pieces from the museum's collection in a fun and approachable way - as well as giving kids the opportunity to electronically create their own works in the style of the highlighted pieces using a drag-and-drop menu.

Parks and Rec departments can also be a great resource for a variety of courses. If you don't mind travelling across the bay on weekends, the East Bay Regional Park district has some wonderful science and nature programs at places like Ardenwood Historic Farm and Coyote Hills Regional Park in Fremont, Crab Cove in Alameda, and Tilden Regional Park in Berkeley - some for a small fee and others free, many on weekends. http://www.ebparks.org/files/RIN_July-August_2011-EBRPD.pdf

For music - many youth orchestras produce excellent concerts for nominal admission fees (sometimes just requested donations) and it can be a cool experience for grade schoolers to see musicians that are not much older than they are. Summertime means that various music and theater groups may be offering free outdoor performances - here's the link to the free Stern Grove concerts for this summer http://www.sterngrove.org/season2011.html
hope that helps! check your library too - ours is a great resource for finding enriching and budget-friendly activities for our family

Edited to add: ranger programs at national parks and national historic sites are also a great resource to learn more about nature and history - the John Muir House in Martinez and the "Earthquake Tour" at the Point Reyes National Seashore are a few we've enjoyed recently. State parks too - a couple weekends ago we visited the Railroad Museum in Sacramento and the docents there are very helpful and the tour was very informative.

My kids do foreign language... which my Husband speaks.
My daughter does Karate.
You can also join various cultural groups.... and they will learn foreign language that way too and meet kids/families that speak foreign languages. Do a Google search for your area/city. Anyone can join these groups.
I also do art with my kids. I have a background in art.
Music, my kids love and we do that at home. We have music things.

And they just need to play too. Not being over-scheduled.
They are kids.

My kids' public school, does fundraising and with that money, they FUND the art and music programs and teacher's pay.
Yes.
The PTA and school, funds this. All successfully.
My daughter learns foreign languages at her public school and music and art. Even the PE Teacher, is funded this way.
Through the schools' fundraising. Only via 1 fundraising a year.
And donations. These are individual/family AND Corporate donations.
My kids' school, has a good community liason/PR person.

Check your park district and see what they have to offer. Ours offers art, fencing, Spanish, French, all the team sports, horsebackriding, the list is exhausting.

Also is there a cooking school in your area?
a craft store like Joann's, they offer all sorts of kids' activities. MY daughter has learned to sew at Joann's. Saturdays
Lowe's and Home Depot offer workshops for kids. Saturdays

Do you have a Droid or an iPhone? They have astrolgy apps. Sit outside and see which stars you can find, Vega, Andromeda, the North Star, the Big Dipper, the planets.

See what kinds of camps there are, it's not too late.

Mine do Girl Scouts, Cub Scouts, Piano lessons, Flute, clarinet, and violin lessons, fencing, art lessons, swim team, church youth group. Keeps me busy and puts a lot of miles on the car. Alot of these are in the evenings.

I should clarify, I homeschool but all the activities from the park district are taught in the evenings as well as in the daytime for homeschoolers.

talk to your teachers. they know about special activities, many on scholarship, for students like yours.
i have my daughter attending a college course for kids. we also found three other special enrichment things, one for gifted kids, that last a couple of weeks at a time. contact your local colleges, museums, and childrens' theatre groups.
even before budget cuts, our school did nothing for the top students. parents began different groups after school(legos, guitar, chess, swimming, computers, and art) but most can't do that.

Chances are, being in California as I am, your school would not be able to fundraise for staff. Our district doesn't allow it. We do offer enrichment courses through PTA at the school, 5 week programs taught by either corporate educators (e.g. play-well tek does the Lego engineering) or local experts. I myself have taught digital photography in these courses. We've had additional art and language classes, some science and crafts. Each course costs under $100 and it's convenient and beloved.

Look into a program called Odyssey of the Mind. odysseyofthemind.com
is an international educational program that provides creative problem-solving opportunities for students from kindergarten through college. Team members apply their creativity to solve problems that range from building mechanical devices to presenting their own interpretation of literary classics. They then bring their solutions to competition on the local, state, and World level. Thousands of teams from throughout the U.S. and from about 25 other countries participate in the program.

It takes strong parental support to make a sucessful program in a school (teams can also be formed through a parks & rec program, girl/boy scout troup etc). OM is a wonderful enrichment opportunity, it allows kids to explore things that interest them, learn to work together in a group and rewards "out of the box" thinking.

I wouldn't overly stress over this. The most important thing you can do for your children is just be there for them. As for enrichment to their education, get them involved in some activities that truly interest them, but don't overdo that. I also find that the Internet is a valuable resource. Find interesting websites and spend some time sharing those with your children. I often get emails with links to fabulous pictures of various interesting places on our planet. When I get those, I call my two daycare charges over to the computer and we sit and watch the pictures. I usually just wait for the boys to comment or ask questions, then give them whatever information I can about that particular picture. (The boys are 3 and 4 years old). We also have looked up websites on things that are of interest to them, such as space, airplanes... and ... well, you probably have a good idea what little boys this age are interested in. You can do something similar with your school age children, and can even challenge them to do some Internet research on their own. I think just being really interested in life in general and in learning new things for yourself and to share with them is one of the best ways you can go about helping them to learn. A good school, in my opinion, is a place where young people are introduced to what learning is, and encouraged to develop a lifelong attitude of learning. If the teachers at your kids' school are doing that, you shouldn't have much to worry about.

The public school I'm going to send my son to has a Spanish immersion program. There's a long wait list and I'm not sure if I want to put him on it. He's only 3 now but it could be a great thing. They teach in 90% Spanish in K, 80% in 1st, 70% in 2nd and on and on. I'm afraid of him getting behind in other subjects. Then again, I wish I could speak Spanish.
Anyway, just wanted to through that out there. If I were you, I might want to keep up with the foreign language. I think it's harder to learn later on. I took it all throughout high school and a class in college and can't speak it. My neighbor has a nanny that comes and speaks to her son and does games with him in Spanish for a few hours a week.
Other than that, it sounds like you have them in a lot of activities, which is great. Piano is something l wish I learned as well.