It sounds like for a long, long time you weren't speaking up about (and possibly didn't recognise yourself) what you want.
I'm guessing you find it difficult to express what you want, for fear you'll be let down or criticised.
What then happened is that after bottling this up you sort of exploded.
Youre now being criticised and I suspect feel both angry with yourself and outraged at the injustice.
The threat now is that you apologise entirely.
When you are ready, if you truly are sorry for the way you expressed yourself you can say that. But you can also say that whilst that was wrong, you aren't going to do free childcare anymore and you hope the friendship can continue for other reasons.
I think this will be hard for you as I suspect deep down you fear people will only be friends with you if they get something from you.
You will need to see how these women react over time to see the truth in this.
Try and think of people whom you do feel safe expressing your needs to.
The fault isn't all on one side in this situation. Adults will expect others not to agree to things that make them unhappy.
Your friends can't read minds and whilst you may wish they were thoughtful discovering your true feelings will have come as a shock, as well as possibly making them concerned about who and how children were being looked after.