Landlord -- I need your input here

Just came back from the rental property(in Stockton, I will share the experience later on), one tenant asked me to sign on the paper that allows them to have some foster kids to stay with them, according to him, all the kids are teenagers. I guess they want to have 3 or 4 kids.
I will definitely talk to professionals with legal advice monday.
Anyone here with similar experience?

I have the following questions:
1)what extra libability we may have?

2)I know foster agency will come over to check the property.
I already told them I will increase the rent if extra cost invloved.

what else should I be concerned? I tried to say no, but I want to help them also since they will have income from the agency.

Landlords, please share your experience and concerns.

Appreciate your inputs here.