If you and your soon-to-be ex are in the process of drawing up your child custody and visitation agreement, it's important to include a section that addresses how your children will divide their time during the summer. You'll need to address things like whether one or both parents will have longer stretches of custody than usual, who will care for the kids during the day and whether there are restrictions on where either parent can take the kids on vacation.
If you already have a plan in place, that's great. It's essential to remember, however, that summer is a time of flexibility. It's typically best when parents can embrace some flexibility, within reason, when circumstances arise that make a change to the schedule best for the kids. For example, maybe a favorite uncle on the other side of the family is coming into town during "your" week with the kids. Do you really want to deny them that time with someone they love?