I am married but not a parent. My sister-in-law wants to go on a holiday with her husband and asked her brother if we could babysit my 5-year old niece for a week. She said she hasn't had any holiday for 5 years, OK well-deserved. My niece likes me (I could feel that as she loves hugging me) but playing with her and babysitting seem like two different things. My sister-in-law shares my niece's routine and the things she likes/dislikes BUT I still feel that there are boundaries that I can't cross as a babysitter! Any tips and advice?