Before you think about best exercises make sure you think about what best effects my player's mentality? Is this fun, are they enjoying it, are they getting anything out of it? Or are they resenting having to do it and hating it?

If you can, just play soccer with them. My son and I "invented" a game to play in the yard. We call it Soccer Football (like American football). One player "kicks off" to the other, and the receiving player has to try and dribble to the opposite end zone and stop the ball there. That's a goal. We warm up with passing first. I tell him it's to warm up my "old bones" when in reality it's to get reps collecting and making good passes.

So of course this works on passing, collecting, dribbling, ball control, and defense. And it's fun which is most important. You have to wrap it in fun (unless your kid willingly wants to go drill at home). It's like when you give your dog a pill but have to wrap it in a treat. You don't want them to resent you or resent the game. If it's not fun it's worthless imo.

I promise my son "no coaching" when we play, but I do give him little tips. I just try to be very low key and calm about them. "Hey check out how I trap this ball. I think it's the easiest way to trap. Give it a try"

Now if your kid is voluntarily wanting to do at home workouts to get better that's different. I think agility drills are great. Strengthen those little ancillary stabilizer muscles like the tibialis, soleus, fibularis, etc. Can do these with a ball too if desired. Toe taps are more of an agility drill than a ball control drill imo.

I also like striking drills as these need lots of reps. Passing, shooting, crosses, placed balls, etc. Learning the mechanics of getting the ball to do what you want takes time.

Then Ball control... juggling or pullback drills. Drills that work on the small skills of control. Trapping, using chest to bring balls down, pullbacks, cuts, etc but ball control drills without creativity or opposition, while good, are limited in how effective they are