My kids are now 25 and 20. I went through the same kind of Mommy guilt when they were little. In fact, I started my own in home company just so I could stay home with the kids when my youngest was 2 years old. I had guilt.
I wanted to give you a different perspective then what you are probably getting from other much younger mothers. Now that both my kids are in college (oldest in graduate school) and I look back, I wish I had never quit my great corporate job with insurance and great pay to be a stay at home mom. It was great for a while but I soon found out that I couldn't work from home very well with kids under foot so I put the youngest in a mother's day out. First it was 2 days per week then 3 days then all week long. That defeated the purpose of being a SAHM - but I found I just couldn't get anything done with kids under foot all day. I needed to make some money for our household. I couldn't afford to just live off my husband's income unfortunately.
We managed to keep our kids in private school throughout their entire school career. It was tough. We sacrificed a lot to do it.
Now we are almost broke though because of my husband's business going under and I am now the sole support with my little home based business which since 1991 had grown tremendously. We can't afford health insurance, vacations, or to fix up our home on what I make.
You never know what the future will bring. When you get to be in your 50's it's almost impossible to get anyone to hire you with a good paying job with benefits. My husband used to make $115,000 per year for a Fortune 500 company. Now because of the economy and banks not loaning small businesses any money his company has gone bankrupt and now so are we as well because his start up company started in May of 2006 - right before the stock market took a dive and took our 401K and our savings with it.
He's tried to get other jobs but every company wants someone young that doesn't cost them much on their health care policy, or someone that they can hire with less experience and train them up their way and pay less to.
So, STAY at work. Use your extra income to buy another car and quit the car pool so you can take off at 3:30 p.m. Use that extra income when your kid gets older to put him in private school. Private school was the single best decision we ever made for our kids. Don't trust them to the public schools. It's not that they are not getting a good education there - it's that they will be associating with kids from all kinds of families - good families and BAD families as well. Your child's playmates and who they make friends with are the most important things when they are growing up.
When your kids are in school you will appreciate that you get off at 3:30 and have the entire afternoon and evening with them - yet still are getting a paycheck and benefits.
Good luck and hang in there.