If we go purely on factors contributing to obesity, plant milks may not necessarily be better. Many plant milks are carb heavy with not much in the way of fat or protein, so it won’t make you feel as full as milk.

I'm not a milk or milk alternative drinker but when I've looked at things like Oatly they seem to have at least as many calories and sugar as something like skim milk.

Kids aren't getting fat off milk. We can a priori expect milk satiety response to be well calibrated.

At least the oat milk brand I like to drink (Alpro) has exactly the same amount of calories as normal cow milk, which makes kinda sense, as they use additional oil to get to the identical fat content :D

So replacing it will not change anything in that regard, we just must be aware that (any) milk is (liquid) food and not a drink. Same problem as with softdrinks or fruit juices.

Anecdata: I regularly drank (cow) milk as a child and now I'm over 2 meters in height. But of course correlation with n=1 is not causation, and I'm sure many people here are equally large without a drop of milk. :D

You can drink a gallon of milk a day if it fits your TDEE.