Notifications whilst phone unlocked

I recently got the Apple Watch series 7 and when my phone is locked can receive all

notifications and reply from the watch which is what I wanted. However my son often has my phone at home for YouTube and I’ve noticed that I don’t get any notifications through whilst he watches it, this is one of the reasons I wanted the watch so I could still see and reply to messages whilst he had it. I saw something about wrist detection but it won’t let me turn it off to enable the notifications to come through on both when the phone is unlocked. Does anyone have any advice please?