My son have large foreskin, that's any problem?

'Large' is undefined: "Large" is undefined. In all normal boys, their penises come covered by their foreskin. They are naturally born that way. As boys grow bigger and older, and go through puberty, the foreskin becomes looser and is able to slide back over and off the glans (head of the penis), which is very important for cleaning. One's doctor can help if a guy did not get his foreskin to loosen during puberty.