He wants to be in the crib/have the crib... because now baby has it and he does not.
Also, he may miss his crib.
But gee, I hope baby does not get hurt/smashed.... by his big brother....
It is dangerous.... must keep on eye on that....
Tell him he is a big boy.... and he has his own bed. Make his bed all special...
Some 'regressions' can occur, when there is a baby around....
For me, I would just really worry that the baby will get hurt.
Like at night, when our older toddler is supposed to be sleeping.... but without your knowing, goes INTO the crib... and either wakes up baby or by mistake steps on him... etc. Or what if baby falls out????
Toddlers this age, do not have fully developed impulse-control yet. And, anytime at night or sleep... he may just get into the baby's crib....
Toddlers... cannot be counted on... to just STAY in their bed, unmoving all night....
Can you just put the crib in your room... for now? Until baby gets bigger or then goes to his own bed?
all the best,
Susan