Or knobs depends on what he likes

IMO the list goes on . I think a nice simple black pull it eh best too bad you did not come here before getting a vanity with all those small drawers and knowing how old your son is would be helpful

The four in the middle are fake ( those are actually two doors) but the 3 on each side are drawers- it’s a big vanity ( the drawers arnt small)….. he is 8 but I don’t want anything to young looking- something that’s modern and will grow with him. I was thinking a simple black too but trying to figure out since there are all different thickness/sizes.

Options are plentiful! Budget will help you winnow down your selection. From the pic, I'd be tempted by matte finishes (e.g. forged iron, matte steel, etc.) over polished one. One trick that helps me figure out hardware finishes, sizes and shapes is to get a few (easy to return) disparate options from the hardware store and see them in my actual space in both artificial and natural light. I don't even need to open the package to get an idea if an option works and then I have a stronger starting point. Etsy is a fabulous source for unique hardware. I'd keep in mind end user and safety when choosing hardware for a bathroom and favour low profiles and rounded edges for knobs and pulls.

Out of curiosity, have you tried the mirror horizontally? With a frame for a bit more "heft", that might work? If keeping the mirror vertical, I think I'd opt for a series of rectangular frames on both or either side. Pictures can easily be changed according to your son's interests. Cut out butcher block paper in standard frame sizes to see what looks best to your eye. I'm not of fan of decorative pieces on bathroom countertops.

Concrete might be an interesting texture but I don't know how practical it is for a bathroom:

Do you have to have handles? I mean, do the doors have finger-holds?

Must say I agree with Mrs Pete. It was my first thought when seeing this vanity. Imo, you can rarely go wrong with "unobtrusive" when it comes to hardware.

I would do large round black knobs:

I'd also add a snake plant to the counter to help balance some of the height and proportions:

For unobtrusive, look at wood pulls to match the vanity. is that mirror a medicine chest? If not, I’d bite the bullet and replace it with a much larger one. Or I would add 2 identical ones on either side like a triptych or so it looks like a triple fold mirror.

In 5 years he'll be 13 and taller. i like what you have and would choose something that would not stand out or detract from the beautiful wood. Edge pulls.

How about a couple of lower, smaller mirrors on each side.

Im a bit off subject here, you have a lot of lighting around that mirror. It looks like there will be not so great shadows on whoevers face is using the mirror. You have overhead, and sides that are directed towards the counter. I think you need light shining onto ones face. I have a lighted mirror and it solves the problem. The bathroom though is really nice. Dont get pulls that are going to be a pain to clean. I have a more grown son and he still gets crap everywhere. good luck.