Disable submit button on Paid Event form (Ubercart)

I have a website where parents can register their children for a sport. The sport has Divisions which are dictated by the age of the child registering. I am using uc_event_registration to accomplish this. When a parent selects a Division to register their child for, I have a node reference added that only displays the children that belong to them that are eligible for that Division. When they don't have any children eligible for the Division and that field is returned empty, I need 1 of 2 things to happen: Disable the Submit button and display a message that they need to return to the previous page to select the correct Division OR Automatically redirect back to the previous page so they can select the correct Division. I need this done today.