why was Gohan such a crybaby as a kid

because he wanted his father

Because he got it from his dad

So Gohan was a crybaby cause he never trained and he dont liked fight. His mother learned him all of these things( to dont like fight, to srudy, to go to school etc.).Goten and Trunks were borned in a time of war and they've trained and learned to be a SSJ from 4 または 5 years.Thats the diference.
I hope i helped u xD.

Hes only a kid

because he was never shown to the world

and picalo was treating him badly

'cause he's a kid.

Because he was 4 and was put in many scary situations when he didn't know how to fight または even take care of himself, and as far as he knew Piccolo was a villain. He wasn't a crybaby, he was having a normal kid response.