Am I in the wrong ?

Ok so today the father of my sons family threw my 2 yr old a party for his birthday that was last weekend I haven’t spoke to his dad in 3 months he took a job out of town and then started ghosting us ( didn’t message me back always ignored me) never checks on his kids or does anything to help we’ll I get to his grandma text him letting him know I was there in 5min before he arrived he texted me telling me he was on the way and he had someone with him he pulls up he and some chick get out of the car ( I’m thinking wtf) He says hi to our 2yr old then comes and gets the 4mo old and tried to hand my baby to this lady I stepped in really quick and took my baby from here and she got mad my ex immediately told me I was being childish and immature and that I don’t want to mess with her ( I didn’t think I was ) I thought it was childish and immature for him to bring this girl or

for this girl to even want to come to my sons birthday party when she doesn’t know him and he damn sure doesn’t know her. At the end of the party me being the bigger person I am I walked my 2 yr old around telling everyone good bye and I even went up to her saying tell daddy’s gf bye and I said give her a hug if you want and he did she was still being nasty and rolling her eyes. When I got to the car my ex came along and threw 300.00 at me and told me to grow up because I told him in a sincere way I was happy he was happy but I really am happiness is important and that’s all I ever want for anyone I cared / care about. Am I wrong was I childish ?! I must be crazy because I don’t think I was