"However, I feel like it would be much easier for most kids to just be raised as the sex they had from birth (without the girls play with dolls and boys with car stereotypes, just let them play with and wear what they want) and being assured that if they didn't feel like that sex they could change it than raising someone gender fluid. I feel like the constant comments and questions and confusions caused by that would be way more stressful than being raised as one gender (in terms of using "he" or "she" and not "they") and switching at a certain point."
Agreed. And claiming that she will raise her son as genderfluid until the age of 18 is unlikely to work out because he is going to have an opinion on how he wants to dress and what he likes to play with way before 18. An a gender-fluid person is someone who might identify as a girl one day and a boy the next. Is she going to force him to wear dresses every now and then until he is 18, so she can say she is raising him genderfluid? It makes more sense for parents to say that they aren't going to raise a child according to strict gender roles and then let them gravitate towards their interests rather than to try and make them live as genderfluid for 18 years.