15 kg stand up mate where you were going with smaller reels. Put a chilly bin with basic gimbal on end and make sure is bit of clearance either side of bait board. Better still clear that bait board away on strike. Little people are same as big people, in fact they are just same as bigger people. 

And that is where I earned the nick name,  before Simon - Sambosi  chimes in .. the”butcher of Tutukaka “ at time,  as fish went 66kg ( in knowledge it was under weight and  I pleaded to be released just before I gaffed it) but she wanted to keep it. And smoked fed all her freinds at AirNZ and made for a great photo on weigh station and helped make my step daughter a gamefisherwoman. Very proud really and she earned that fish,  hooked up in a comp 5 minutes before stop fishing and it put up a good fight. Caught bigger fish but that was memorable.

My son is now 24 and I started him fishing at 3 1/2 and game fishing at 8. Here's what I did and with the benefit of hindsight would do again for the game fishing.

Kingfish and tuna (skippies/albacore) are great to start kids on as they are more abundant and easier to hook when you find them. This also teaches technique.

Get him his own set - 10 or 15kg line class. My son used a vintage Penn 30 International that was originally his grandfathers and this handled everything from kings through to tuna and marlin. The rod is just as important, good action 10-15lb line class. Think about shortening the butt so he can comfortably use it in a harness, particularly on larger fish. This is his set so anything hooked on it is his responsibility and the other sets are for the adults.

Let him pick his own lure and make him responsible for everything from making sure the hook is sharp and the leader is not damaged, clipping on to the main line, deploying and making sure it's running ok, watching for weed etc. This is important. It will keep his attention up and teach him how to catch fish, rather than how to wind one in that you have hooked for him.

Most important. Make up a tether so that he cannot go overboard. I always used auto inflating life jackets that had a lifting ring on the back strap with the other other end secured around the centre rod holder on the rocket launcher.

A lot of the fishing I did was just the 2 of us, especially when he was really young because I wanted to be able to cut the day short without disappointing other crew. It also provides the opportunity to make sure he knows how to properly use the vhf and drive the boat. You never know when he will need to - in my case it was when he was 10 and I went overboard on the way home one morning after the weather deteriorated. Thankfully we always wore lifejackets and my boy knew enough to safely turn the boat around and save his old man.

Thanks every one that's chimed in so far, I have managed to source a couple of tiagra 20 reels that I'm getting spooled with braid then I will make up a couple of short top shots, I think I will just start at 10kg and do a few tests at that to see how they go, what's a better fish to test out the setup with big stingrays in shallow or sharks, both seam like they should be pretty easy to hook and should put up a fairly sustained long fight.

Also Shaneg the chilly bin seat idea sounds good, I just can't exactly picture how it works, are you using a shoulder type harness or a bucket type, do you have a problem with it sliding around at all?