While no personal experience, the fillet knives from
G L Drew
look very good. I think most of his stuff is made from carbon steel, so keep that in mind if your kid isn't comfortable with that steel type.
I like the look of the Martinni fillet knives but the lack of a front guard or good finger stop is not my favorite design, on top of the handles tending to be slick. Depending on how old your son is, that can come into play.
I like the design of some of the kershaw and buck fillet knives for other factory options, but not a fan of their use of 420J2 steel, which is just soft and I'm a little bit of a steel snob. Plenty of people use it and realistically, for occasional use it's fine. Touches up really easy. This is where I prefer the morakniv fillet knife though as the steel is better and my hand likes their companion handle style.
Now, not sure what type of fish he's filleting, I have a strong preference for larger blades so I tend more towards the broader and longer styles, limiting what interests me. This is because occasionally I'll catch and clean a pike and I find the longer blade is a lot easier to get the y-bones out of. Something like the 9" curved fillet knife from Kershaw is what I'm talking about. I'm also really used to using longer kitchen knives so feel comfortable with a 10" blade down to bass sized fish. I'm currently trying out a Kastking fillet knife, which is probably something generic with their name on it, but it comes in orange and orange is the sharpest color.
I have a different knife for panfish, as proper knife nut.
Last recommendation would be bubba knives as they seem to really focus on fish processing knives. They are a utilitarian look, but I don't think they're ugly, exactly, especially if you're fine with red and black colors.
