DD was 2 weeks old - she had a sleep over at BIL's house while we we removing mould in the house. She has been left numerous times with family over her 4 yrs.
DS was about the same I guess. MIL offered to take him over night so I could have a sleep in LOL (They live upstairs, our house is a duplex) I also leave him often with family when I have things to do which are alot easier without kids in tow.

My IL's offer to take them alot so I take them up on it. The kids LOVE it & it gives me some time to myself. I do miss them when they're not with me though.

Each to their own. I wouldn't change the way I've done it.