Kids Paint Advice

Most finger paint will not stick to a canvas. Finger paint is best for paper products. Acrylic is meant to stick to a canvas and works the best on a canvas. There's many acrylic paints on the market and you should always use only child grade acrylic that is non-toxic and has the conforms to ASTM D-4236 on the packaging. This means it is a U.S. approved non-toxic paint tested and not harmful to children.
Creating a gift one time you should be fine using any type of non-toxic acrylic. But if your children plan on using on a regular bases painting you want to use only child grade paints for kids. There are some acrylic on the market that are safe for kids to use.

I don't have any advice about the type of paint.
But- your 3 1/2 year old might be able to use a paint brush just fine.
My son has been using one since he was 2.
Crayola sells bigger ones just for little hands.

Acrylic paint is okay on skin but could be toxic (depends on the type/brand). Also acrylic is washable when wet but permanent on fabric when dry. I have let my kids use both (they are 2.5 and 5 now). Fingerpaint is fun but the results are sort of transparent and not as strongly colored as regular paints. Crayola washable tempra paints might work for you--they are washable and non toxic but have better color than fingerpaints. but tempra paints are matte, not shiny. You could always get a can of clear acrylic spray and put it over the paintings when they are dry (and the kids aren't around). Also fingerpainting is fun but so is playing with brushes or making sponge shapes to stamp with. I like to do things with hand or footprints but it can take a few tries to get a nice looking print with squirmy kids. Good luck and have fun.

they have crayola paint in the crayola paint brush. It works great.

Many acrylics are toxic. Use a paintbrush if you are going to use it. A three year old can use a paintbrush. Tempura paint is non toxic and is what you should use for hand/feet painting. But tempura won't bind to the canvas. I agree to use a clear acrylic spray to bind it to the canvas.

EDIT: Most artist grade acrylics do have a level of toxicity, although it is not nearly as high as oil pigments. I have taken several college painting courses and have had to research the toxicity of the mediums I use. Craft acrylics are different, they are watered down and do not have the concentration of pigment that artists grade acrylics do. So to make a blanket statement that all acrylics are non toxic is a misrepresentation.

Most acrylic is NON TOXIC- I know this because my son when he was a baby ate a bunch of red acrylic paint and we freaked out and rushed him to the emergency room. He was fine and the doctor told us acrylic wasn't toxic. I also talked to my mom about it when we got home(she is an artist and art teacher and uses all different mediums) she said that most acrylic's are non-toxic- it's the oil paints that you need to worry about.
The typical craft acrylic is perfectly fine to use- just put on clothes you don't mind your kids getting paint on. Acrylic is also used as a face paint( it dries quickly and washes off easily) I dont' know how well finger paint stays on canvas- I haven't used it before on canvas- but it is more transparent than acrylic. Have a bunch of wipes handy and cover your table with newspaper to keep the paint off of it. I have large t-shirts that I put over my kids clothes when they paint. And just have fun! Kids love to paint!
~C.