I feel like my son gets treated differently...

So my husband has a 2 year old daughter and we've been together over a year now. We have a 5 month old son together. His mom gets the grand kids sometimes on the weekends which includes my husbands daughter, and his nieces 8 and 9 years old. So she goes to my husbands exes house to pick up my step daughter and picks up the other 2 girls and they all stay the night but she never asks for my son to come over. He's the only boy, her only grandson. It really hurts my feelings that she gets my husbands daughter but not our son. I mentioned it to her and she said "well it's all the girls." Yes but he's the only boy. If their were other grandsons I could see getting the boys and girls separately but it's always going to be all girls if he's not there. I feel like he is being singled out. And it's not due to age, she's been having the grandchildren stay the night from like 2 months on. What do y'all think?