If your goal is to make the characters look younger then you have to resize some proportions.
With age the head goes smaller compared to the rest of the body, the hands go bigger, the body stretches up, the nose becomes thiner, the eyes smaller, the head less round.
To make them go younger just invert all these parameters.
Try to make their nose less thin, even bigger. Also, resize the head by 8% or 6%.
Size is very important for make believe. In anime, all the girls are smaller than the boys, like in real life. What you see in anime girls are, besides the big eyes and small nose/mouth ratio to the rest of the head, is features that don't do much with height. Instead, the anime girls are rather small. What they have is disproportionate, or over exagerated feminine features like big breasts, thin waists, round glutes (unless the fetiche is petite, where the girls look like early teens or even childs).
I guess from that image that the characters are over 1m80. Is that your goal?
Also the thin nose makes them rather older by a 10 or 15 year factor (if your intention was 16/18 teens).