I'm with marydean. Tell the WHOLE family that the money is missing and it would be appreciated if the person responsible would just put it back. If not by the end of the week - confiscate something worth $10 of each. You could even confiscate something from the whole family (exept the b/day girl of course), just to make sure that you are fair.

As for the small change going missing - make a "game" of it with the smaller children. Buy a piggybank (that is sealed shut at the bottom) and teach the kids to throw the small change in there. That way they know what to do with money laying about the house. We had that as kids and I tell you, you had to really search our house to get a bloody 5c laying about!! At the end of the year (chrismas time) we would break it open and mom would treat us to ice-cream and a movie. I think she may have just added some $$ sometimes - a year's worth of car-change could not possibly pay for 5 wafels and 5 movie tickets ... could it?? *off to find jug for loose change - just as a experiment*

Good luck!!