Problem...my 20 month old found my stash for the baby, and now he was?

Toddlers often do things like this when there is a new baby coming. They feel threatened. And think that if you have to take care of them the same way you will the new baby, they will get the same amount of attention! Don't give in, let him do it, and eventually he will get tired of it, try to get him to help with the new baby as much as possible, and he will step into the role of "Big Brother" instead on trying to go back to being the little baby.