my kids often get left with MIL and SFIL, Also with my mum and sister etc (like this weekend, jess went to my mum and sisters place as Kat was in hosp and we couldn't have Jess with us). I love having a bit of a break and I totally trust my family (well most of it anyway) including inlaws. I think it's up to how much you trust them and how well they know the kids plus their relations with you and the kids. This will sway any decision........ Ultimately it's up to you. If you are not comfortable with it for any reason.....then don't hesitate to say no. They are the most precious bundles in the world and it's better to be over protective than find out/have something go wrong!