Pro-tip: If a kid is getting promoted up to a different school (K, Middle, or HS), the previous summer, take them over to the new school and kick or toss the ball, bike around, or have a picnic. It's unlikely the buildings will be open, but in most public schools, the outside areas often are.
The first week in the new school will be a breeze vs kids who look like they're ready to throw up.
This also works if moving to a different home, city, state, or country. Spend as much time around and near the school before the first day, just playing.