Your lip smaller volumes are not where they need to be atm. I'd exaggerate how realistic they are and nail it anatomically correct before "softening" it to make it stylized.
As you havent give any specifics on what kind of stylize head and I cant really tell if it male of female I have to assume few things and use my observations Most sterilizations that i have seen are based on babies or little kids anatomy due to their cute proportions so my suggestion for you is to lower eyes below mid line of the head and to keep cranium bigger then jaw/face this is pretty much how you show age[big eyes small features less depth and lots of fat are other useful tools ] Using references of real kids will be extremely beneficial once you understand what are you trying to do will be easy to modify and stylized it to what ever you please
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I got this from Felixenfeu