L.A.
If you want to do this as a "pilot project" here are some thoughts for doing this small scale, just to get your feet wet.
Find a charity that needs short term volunteers. i.e. if the American Cancer society is doing a telephone fundraising drive. They might already have a space and date and volunteer facilities in mind.
in conjunction with the event organizers, set up a meet up, or post on local area bulliten boards,etc. that you want to orcestrate a group of SAHM/Ds to man the phones. You, and some tween/teen mother's helpers then man the show with adult supervision ratios in line with area daycare. If you want to do this for say 4 tuesdays in a row, for a 4 hour time block/6 hour time block. See how you like it, see how it works for you, the parents, the organization. then scale it up.
By all means speak with a lawyer.
If you are looking to facilitate your own volunteer efforts in this fashion ask organizers if they might pair you with another mom. You might be able to split fees for a babysitter, or take turns taking all the children so the other gets a turn at volunteering.
good luck to you and yours
F. B.