L.G.
Phew! I'm tired just reading this. LOL (kidding).
I am a single working mother of three kids, ages 9,9 and 10 years. I have been a single mother since they were teeny tiny. So somewhat of a logistics expert.
First bit of advice. Talk to the 4 and 7 year old, tell them you are going to school and that they are going to help you by being a part of team Mommy. This makes them feel part of the solution, not part of the problem. I call my kids team. "Team need your help" "Team we gotta get out the door now etc"
Second, Prepare absolutely everything you can at night before bed. Lay out the clothes, sweater jackets. Pack the backpacks and diaper bag. I don't suggest putting them in the car at night, because you'll need to add lunches and baby milk in the morning.
Third, and it will be difficult at first but the 7 year old and the 4 year old can dress themselves. 4 year will need help with zippers and what not, but can do it. Mine started that young. That will help you out a lot.
Fourth, get up at least 45 minutes before you have to wake the kids, pack the lunches.
I won't lie, unless you are one of those morning people (I am not) it will be really challenging some mornings but the more preparation you do before morning hits the easier it will go.
And Way to go on going back to school, that is fabulous.
Good Luck
L.