You want to dig into the specs of the boots to find where money is being saved. To produce a boot cheaper money needs to be saved somewhere. Usually on Jr products that may be in shell and cuff materials or liners as these are areas its easy to save money.
Cuffs will often change from PU to PP for example. PP is lighter which is desirable in Jr products but its not as durable, but often this may be less of an issue then it would in an adult boot but something worth considering if you are buying a large size in a Jr boot.
Liners will often be more basic and forgo many of the "custom" features. If they fit well great but there may be less chance to change them if you need work doing.
So if you look at the specs of the AllTrack Jr 80 and the Alltrack Pro 100 they are similar.
View attachment 1001884
View attachment 1001885
Shell and cuff on paper are the same. PU shell and PP cuff, but it does not say any more than that really. There is a possibility they use regrind in the Jr model which will be a slightly less high quality product. But more or less they look similar but cant really be confirmed from just this.
The big difference is the liner. T4 on the Jr and T3 on the 100. So the adult boot get the better more custom liner.
So in this case on paper not a huge difference but the adult boot does get better specs which in most cases will be the case but if the Jr boot meets your needs and fits well it could still be a good choice.