Immersive Children fixes the problems that Non-Essential Children and past killable children mods introduced: disabling child animations that required the IsChild condition. Disabling the child flag (what the IsChild condition is dependent on) in the child races prevented unique Hearthfire child animations from playing such as girls playing with dolls, laying on the floor and kicking their feet in the back, pouting when being told to do something they don't want to do, kneeling, etc. By disabling the child flag, past killable children mods allowed children to use "adult-only" furniture, idles, and crafting stations which caused them to grow because of the RaceToScale function. Non-Essential Children prevented this size-scaling by preventing them from using MOST furniture and crafting stations but also unintentionally caused them to not be able to use chairs AT ALL so if you ever played with Non-Essential Children on and watched the children during the day, say for example Lucia, she'd never sit down on the benches around the Gildergreen because the ActorTypeNPC, which furniture are dependent on as an Interaction Keyword, was removed from the child races. TechAngel just didn't specify which mod they were referring to.