It sounds like your son might be pretty laid back, if he is not fighting the crib, so maybe he would be equally accepting of the move. I would go ahead and do some switching around if it were me. I would for sure move the 16 month old to the crib, I cant imagine that thin mattress being comfortable on his growing body for much longer! Sometimes, in a family, we have to think about the betterment of the whole family, not just one child, and since you already have a bed for him, I say go for it. Maybe try asking him what he thinks you should do about it. Saying something like, "son, your little brother is getting too big for the play pen, and needs a crib, but we only have the one you sleep in. Since you have two beds, how do you feel about moving into the big boy bed, and we can make the crib a special place for your little brother..." And, while I agree about making it a bit of a big deal, I would not go overboard. This is just something that needs to be done for the family, and the more attention you give it, the more likely he is to react. Obviously, you are the only one who knows your children, this is just how I would handle it. Good luck!