You need to kill the mobs, near to where the alts are standing for them to get creditted with xp. I have boosted 2 alts all the way up to lvl 51(so far) using my 80 hunter. In lower lvl dungeons i get my pet to go around and tag as many mobs in the dungeon as i can, then call him back to me at the start of the instance. I stand about 10 yards in front of the alts and AoE everything down. The alts gain about a level per dungeon clear on average. The alts are currently at about 20hrs /played at lvl 51.

Currently doing Strat to level them, which is a bit more tricky with my hunter. I just chain pull everything and have the 2 alts follow me. Might try Scholo soon for some variation.