Yeah, sorry YABU.
Of course it is wrong to stereotype and assume that all boys are overtly physical and so on... equally, it is wrong to stereotype girls and assume that all girls are bitchy, sneaky etc... Therefore, I agree that it is wrong to assume that all boys are 'awful' as you said in your OP.
However, I don't think it wrong for some women to note that they would struggle more with a son or a daughter. As another teacher and former play worker, I 'get' girls far more than I 'get' boys. For that reason, I taught in a girls' school for many years and think I am a better teacher with girls. I now have 2 DDs and think that I'm probably a better mother to daughters than I would be to a son. I am quite girlie myself so we enjoy having girlie days together, in our free time, we enjoy doing all the arts and crafts together and all that kind of stuff (They're into all the traditional girly things - Ballet, gymnastics, HSM, pink, clothes, shopping...). Further, I have a friend who has a son and she is an amazing mother to him, in a way I know I could never be. But she enjoys being outdoorsy, kicking a ball around etc (For my DDs outdoors constitutes making daisy chains and doing cartwheels!)I have another friend who would hate to have DDs - she hates all things pink and girlie, and so she says she'd hate to have daughters, and much prefers having sons...!
It just works both ways - Some people get girls better, others are better with boys - just in life some women prfer to have female friends, whilst others prefer having more male friends etc etc... It is perfectly normal to have preferences, the only thing I think yanbu about is if it is voiced in a rude manner that puts down boys or girls - because neither gender is better than the other, they're just different that's all.