what do you need to prove you are the primary caregiver of a child?

"receipts for everything you buy pertaining to the child, and that means for all the bills you pay, all the food you buy, all the clothing, everything! if you aren't the parent, keep track of how long you have the child every day, keep a notebook or log of the things that who ever else has bought. those are jsut the top things i can think of."