Without more details it's hard to say whether the person could be unaware that they're under-performing, but in my experience it is always better to bring a problem to a person directly and give them a chance to fix it themselves than to go over their head right away.
Is there some objective way to measure the amount of work everyone on the team is doing, say a number of [x discrete products] completed per week? If so, I would suggest approaching them as non-confrontationally as possible, noting that their production is significantly behind other members of the team--using concrete numbers rather than a blanket 'you don't work enough'--and asking if there's something you/the other team members could do to help get them up to snuff. It's possible they need more training or aren't aware that they're that many orders of magnitude behind everyone else and just need to put in a bit more effort.
That said, if the person isn't receptive to constructive criticism and is genuinely a drag on the rest of the group, there's nothing childish about making sure that's known. Just make sure everything is above-board, that when you bring this to your boss you keep your criticism as a professional and not personal issue, and that the person in question has had ample chance to rectify their behavior first.