When this stepmom is concerned, she asks Reddit:
I (34f) have two boys (10m and 8m) and my husband "Dirk" (40m) has a daughter from another relationship "Gwen" (just turned 6f).
We are a healthful household and we teach moderation and controlling how much we take when we have treats. We are also very active and every day strive to get the boys moving.
However, Gwen is only here two weekends a month, and her mother has the exact opposite attitude. In all honesty that woman's blood type is probably ketchup. Similarly, Gwen is about 20lb heavier than a 5 year old girl is supposed to be.
It makes me sad for this child and her health so when we get her I try to teach Gwen about healthy eating and moving around. We have the boys play with her so she's getting active, and we make a distinction between foods that are healthy and ones that aren't.