Baby shower etiquette HELP!!!


So my son has a little girlfriend in school, he is 7. So I have become friends with her mother for play dates and such and my mom invited her to my baby shower at my request. Now my son may be at the shower or may be out fishing with my BF we don't have a solid plan. Anyway this girls mom just told my mom on the phone that she would be bringing her 7 and 2 1/2 year old daughters with her. There will be no other kids there and I think it is odd she just assumed this was okay. She's a really nice woman and my mom and I are just trying to figure out how to tell her it's not really a kid thing??? I want my son to either be involved in the shower or out bonding with my BF and I know he won't do that if the kids are running around :/