When you send a payment request to your team, you can enter custom amounts for different team members. For parents with multiple children in the same team, you could request a larger amount from the parent in comparison to other parents in the team.
When you go to the 'Collect Payment' page in your Teammo account, fill in the details as usual. Once you've filled in the fields above your team member list, you can manually change the amounts people are required to pay in the Amount field to the right of each person.
In the scenario below, the team manager requires $10.00 from every parent. However, David Smith has two children in the same team, so the team manager has doubled the amount requested for him ($20.00).