As already noted, it's good for all children to have relationships with men and women, but that's so they can grow up to be a well rounded human being. What does it even mean to "learn to be a man?" How about we let kids grow up to be whomever they actually are and leave the strict gender roles off the table because forcing boys (or anyone) into tight little boxes that may or may not fit causes more harm than good.

Men Describe What It Takes to Be a ‘Real Man’