We are expecting #2 in a few weeks

I’ve been slowly setting up baby items around the house (bassinet, swing, etc). My son really wanted to get in the swing. I let him put his baby doll in it and swing her. Today we had the stroller bassinet on the floor and he climbed in and started fake crying. We pretended he was the baby for awhile. It was actually really cute and funny. But I’m not sure how to respond? Obviously when baby comes he won’t be able to get in with her... I want to validate his feelings about wanting to be the baby while also keeping the baby safe

Anyone have experience with this?