Dressing son as a daughter

Raychel • 👩🏻🧔👦🏽👶🏻🤰🏻
Okay let me start off by saying I have no problem with transgender people at all! I'm not the type of person to ever hate someone for expressing who they are. Be yourself at all times. However I have a major issue when you push what you want onto someone who can't make their own decisions. 
My brother in law and his gf have 3 sons. With their 3rd son they were hoping it was a girl but obviously he came out a boy. They gave him a sorta girly name which didn't really bother me because it's just a name. No biggie. Anyways as parents they decided that they wanted to dress him as a little girl and treat him as a daughter because that's what THEY WANTED. This is a huge bother to me because he's only 2 and can't really make his own opinion. I understand if he came to them and said he identifies as a girl but to push what you want on an innocent child. That upsets me! Am I overreacting for being upset about this or should I just let it go???