I work at a daycare and learned about foster care but i still have ????

im a helper at a local daycare and the kids there are mostly brats but they will listen when u use a certain tone with them. but today i learned that the reason whey half the kids there are so misbehaving is cuz they are in foster care and cant be ed until they get legally adopted?? why is that?? can anyone explain a little bit about foster care please and thanks in advanced!!