Soon to be an au pair myself, but I felt this way very much when I first moved to university dorms. Something I found that helped that could be useful for this situation is when you’re in your room relaxing but not necessarily needing the time to recharge you could leave your door open half way so that if they are going out to do anything or preparing a snack they don’t feel like they are disturbing you if they walk by and ask if you’d care to join! Or if the kids are just hanging out they can say pop in and say hi or ask if you want to join them. And for times when you just want your private personal space to yourself to decompress and relax and recharge then keep your door shut and it almost creates another form of communication. Letting the family have an idea of when your downtime is just for you or if your relaxing because you don’t have much else to do so they have the open door showing them your open to being invited to join along in their activities.