I completely agree with Larra. Kids under about 10 don't have the cognitive ability to make thought out decisions on their own. Some can as young as 8. But 10 is average. Until they can choose for themselves, you are only imposing your will on them. And they are not capable of knowing how to take care of them properly. He may only be 16 months, now, but when he gets old enough to go about on his own, he'll probably be getting dirty and rolling around in the mud like kids do. You'll have to either keep them from getting dirty regularly, or washing them every day which will cause a ton of problems when they are mature (which they will be once he gets to that stage).
Ok, I've said my peace.
NEVER go to a salon. I won't say all, but more than the majority of salons destroy locks. Beauty schools tend to not teach about lock at all. If they do it's for fashion, not for health. They use wax, gels, creams, interlocking, crochet hooks, felting needles, and a whole slew of other damaging processes to create the illusion of locks. I was told to apply wax 2-3 times a week and not wash for 2 months. When I finally did, 1/2 my hair had rotted away and it just melted off my scalp under the water pressure. The twists will probably only hold until you wash his hair. they aren't meant to hold longer than that. They, like all starter methods, only create a rough blueprint of where his sections will form. NEVER retwist them. That puts too much torque on the scalp and rips hair out causing weak roots and traction alopeica. That is a condition that leads directly to baldness. You don't want a toddler to start going any balder than they are already