Sleeping after night shifts when a 7 year old is home all day for the holidays

Night rota this fortnight. I get home around 8 in the morning and need to sleep till about 2. Our son is home all summer. Family at home look after him, but he's 7, the flat isn't big, and by 10 he's knocking on the door 'just to ask one thing'. Shift-working parents, what has worked for you? A sign on the door, a fixed time he can come in, white noise, sleeping somewhere else?