A mother & father brought me their baby to babysit and have not been back in 3 days? I want to keep the child, I feel they have abandoned the child?

You can't keep the child. If you can't reach the parents you have to call Child Services and let them take over. If you don't you could be charged with kidnapping the child. The parents can say anything.

Assuming this is the US , this is a child, not a puppy, they are not just yours to keep if their parents don't come back.

You need to contact the police or children services