El chico necesita banarse with a tilde over the "n" in banarse.
You can say "¿eres un niño?"
Good boy = Chico bueno
"amante"
papa
you say it like this: clease boa
Niño guapo
Mal muchacho.
Niño chicita
Venga, chico.
mi hijo
"Needs to" in Spanish is "necesita". It is pronounced "ne-say-SEE-ta". Please see the Related link below for confirmation of the translation.
Depending on who you are asking it may be either formal or informal in spanish. If it is formal you say, "Pueda usted bañarse." In this case it sounds as if you want to ask a person you are familiar with to take a bath so you would say "Puede banarte."