DS2 is 3.8 and will be sleeping over night at my PIL for the first time tonight. He has slept there in the day before to have his after lunch nap and his brother and sister will be staying too. When is the best time to tell him and what do I do if he gets upset when it is time for me to go and/or says he doesn't want to stay? I wouldn't leave him in that case but tbh DH and I really need a break. TIA.