I guess I'm in the minority - but I support mothers working outside the home. Obviously you do need to consider the financial pros and cons -- can you make more than enough to compensate the day care fees and additional gas expenses?
But I see that, if placed in a good and nurturing environment, children excel in day care. As an example, my daughter has been in formal full-time daycare since age 1 (she's now 6) and I have a nephew that is a year older, but was at home until he went to Kindergarten. I saw him a xmas of that school year and he was so proud that he could count to 20 and could do 1-5 in spanish. My daugher, again being a year younger, could already count to 100 and do 1-10 in spanish. So she was much more advanced in her learning because she had more structured play at day care than I would have done at home. Also, she started Kindergarten this year and that first month she had a few classmates that sucked their thumb or refused to do their assignments at their desk (they prefered to sit on the floor) and they had stay-at-home moms up until the first day of school. They were not prepared at all for the environment.
I've met stay at home moms and they talk about watching TV shows when their kids are still up and they just have them play in the other room, or things like that. Since I have limited time with my daugher, my time is with her until she's in bed. No TV, no laundry, etc. My evenings are spent with her. So I have just as much quality time with her than some stay at home moms that spend the time making dinner, doing laundry, running errands, etc. So again, I fully support quality day care and do not feel it detracts from the special moments with your children.
I would suggest taking this in phases. Phase 1 would be putting the kids in a mother's day out program where they are in a day care setting for half a day (10-4 I think is standard) once a week. You'd just need to make sure it's a program that teaches the kids things through play, versus a free-for-all baby-sitting service.
Phase 2 would be part time day care - either half days or a few full days a week. This would give you time to do a part time job for that extra income and adult interaction! Your 3 year old will need pre-school before Kindergarten anyway, so this setting can also prepare him for his time away from you and the structure/tules he'll experience in the classroom.
Phase 3, if needed, would be the full-time day care. This could very well wait until your oldest is in K since he could do full day K or an afterschool program, while your youngest adapts to a full-day program.
This was probably more info than you needed, but I had a lot to say! I wish you luck.