Whoever their parents are should be paying you child support first. But if you don't have legal custody of them .. I doubt you're going to get aid for that. It's your choice and you shouldn't do it unless you can afford it. Don't short change your family to help someone else's.
If you are babysitting for someone, then you need to be paid for those services. What was the agreement when you guys decided to watch the kids? If there was nothing in place, why wasn't there mention of a fee when you guys began this?
Call around to daycares in your area and see how much it would cost for these kids to be in daycare. What kinds of services do you guys provide - meals, snacks, outings (trips to the zoo, going swimming, etc.). Decide what a reasonable amount would be to charge.
Then approach the person that you are babysitting for and work this out.
The lesson to be learned here is - everyone should get paid for providing a service, unless you are extending charity to someone. There could be hard feelings coming out of this because you waited so long to ask for payment, so be aware of that going in.
If you are looking for money from the state you would have to qualify as foster parents and the children put into the foster system. My niece has been through this and the only thing she qualifies for is food stamps.
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