Unfortunately you are ‘allowed’ to! I’ve been in and out of hospital with my daughter since she was 4 years old (teenager now) and we’ve seen loads of children left alone! One point there was a baby alone for the whole time we were in there (4 days) the nurses would just FaceTime the parent who would talk to the baby every now and then and the nurses would prop the baby up out of bed every so often but the whole time we were in there, there wasn’t any visitors