I was thinking more about little kids in his nursery/pre-school group or neighbours' children? Just a thought - you know the old saying 'monkey, see, monkey do' - if a child sees something gets results they'll mimic it.
Tbh if he's eating normally, gets plenty of sleep, has sufficient energy and you jolly him along, it's probably just a phase.
Why not mention it to one of the nursery staff, see if he's happy there, not saying he's getting picked on but it could be a growth spurt making him tired and crabbit.
Hi all im prob just bein to observant and nothin to worry about my Ds is 5yrs old turned 5 there in febuary since then hes became only way to describe it as a cry baby never had any bother before he crys over thw simpleist of things if his sister gets asked to do something and he doesnt he crys if hes asked to put shoes jacket on he crys n moans if he doesnt get what he wants there and thwn he crys im at a loss I dnt know if its thw thought of change he starts primary 1 in august or if his is just a phase anuone any ideas please x