To see if it's active, open your Character Generator and click the Kid tab. If you see multiple clothing and hair options (instead of just one or a blank head), it is correctly installed.
you need to fill (e.g., main party members, background NPCs) RPG Maker MV - Add-on Vol.4- Kid Generator Parts
The pack contains a comprehensive suite of facial and body features designed specifically for the child character base: 22 Front Hair and 22 Rear Hair styles. Facial Features: 15 Eyes, 14 Eyebrows, 19 Mouths, 3 Noses, and 2 Ear types. Clothing & Accessories: To see if it's active, open your Character