Hey ladies (and gents?)

I have a friend who has a 5 year old son. My son is 3 months old, and I am exclusively breastfeeding him. So the 5yo didn't know what breastfeeding was until I had my son, and he loves feeling/being helpful.

Every time they are at our house and I have to feed the baby the 5yo gets very uncomfortably close. Like, even if he's occupied doing something else as soon as the baby needs to eat hes literally so close he's touching me. I'm not sure if this is normal for a 5yo or if its something his mom should correct or I should correct. I've never had this issue with a child before and I'm not sure how to say to him that it's uncomfortable or to his mom that she should be correcting him when hes sticking his face next to my son and my boob.

Ive tried telling him 'the baby is eating now so we need to let him eat and do other things', but his reaction is to ask me to play games or sit so close he's touching me and say 'okay but if the baby needs me just let me know'. And just sit there.