J.:
If I could have worked only part time until my children were of school age I would have ( I am a professor and would have given up any chance at tenure had I quit completely or tried to work part time.) It is true that you cannot get that time back both in your career and with young children!!! I also would have had a difficult time with this decision as I love my work; I would have missed it. It seems to me if you can stay home until your youngest is in first grade and then go back to work (maybe part time at first) that this would be a good balance.
I also happen to be someone who grew up poor and when I had kids I wanted to know that if anything happened to my husband, that I would be able to support my family financially. (My mom could not.) (When I was a kid I saw first hand how hard it was for some moms to get back into the workforce when they had to and I did not want to go through that...this is a very specific example, but it is one of the things that drove me to seek a career.)
I do make sacrifices in both aspects of my life and I am honest about that, which is difficult. I was being pressured into taking a high-level leadership role at my college and I had to mention many times, and sometimes with great force, that I could not accept due to my family responsibilities. It was very hard for me to openly say this as I feel that women in the work force are somehow supposed to deny that they have other, more important obligations. I have been slammed at work, mostly by other women. When a man declines to work late because of a child's need, he is a hero. When a woman does it, she is seen as using her private life to be lazy.
I have also felt guilt for the things I have missed. Now that my kids are older (12 and 8) it is easier and I can even talk with them and see if they feel bad when I miss things that SAHMs are able to participate in. Generally they are okay, but sometimes I feel very guilty. I feel very fortunate that teaching is a career that tends to allow me to be home when my kids are home, for example. Still, I know that if I did not work so much, I would be more present for my kids.
On a slightly different note, I think my marriage is stronger because I work, but that is a very personal thing...I think some marriages are stronger because one parent is able to stay at home (my best friend is a doctor and her husband is the stay at home parent and it is the perfect situation for their family). My husband and I work in the same field and just today he was feeling upset about something at work and I was able to help him and he said "I am so glad I am married to someone who understands what I am going through right now." That made me feel really good about my decision...especially because I think sometimes when we are raising young children, we can forget how important it is to focus on our marriages (but maybe that is just me).
You sound like a really great mom who is doing some good, thoughtful reflection on this. I am sure you will find a solution that offers your family the best balance. Good luck.