OK - I have a number of thoughts.
There are very, very few truly working chocolate labradors - and those that are truly working are highly sought after - leading to very long waiting lists and quite high prices. I guess it is more likely your daughter's chocolate is showbred (ties in with him being a big dog, working types are usually less heavy) with an injection of working ability from somewhere.
There is absolutely no chance that his breeding - whatever it is - is responsible for his pulling.
Your daughter is responsible for it - entirely, unfortunately. She is letting him get away with a behaviour - and for him, every time he pulls, he is reinforcing to himself how well it works. In the dog's head, the behaviour is working. Every time. He is pulling and getting where he wants to go. So he'll keep on doing it.
My first step would be to stop putting him on a lead to go anywhere. Drive to a walk. Break the cycle of pulling hard = lovely long running about walk. Dogs make links really, really quickly.
Start some intensive training - it matters not at all what lead you use, and harnesses, in my view just make it more comfortable to pull. It's no coincidence that harnesses are used by sledge dogs and horses. Spend 10 minutes, every day square bashing on the lead. Use treats as a lure to keep him at heel - and use the work heel as a positive instruction, not as a bollocking. Train somewhere neutral - if it's away from home, drive there, and don't use the place you take him for a walk.
Also don't hype it up before you go. Matter of fact, and not a single clue before you go. Not a 'come on then'', or a particular coat or lead, nothing. Start afresh and separate it entirely from the walk. Completely.
And most importantly of all, don't allow him to pull. I always, always spin around, change direction - anything to surprise - at the first hint of a young dog pulling. The same applies to your daughter's nine month old.
It does sound as though his brain isn't well used - the stick obsession points to it. Labradors have active, sponge like brains and using them via training of some sort really helps with their behaviour.