DCL does not require a child to be fully potty-trained as long as he/she is at least 3 yrs old. You will be required to return periodically to check/assist the child; maybe every 30 or 60 minutes. If the child is 3 yrs old, you also have the option of using the Nursery onboard, though that does require reservations and an extra fee.
I haven't used the WDW childcare clubs, but I do believe they require potty-trained.
When we did DCL 4 yrs ago, my 3.5 yr old was sort of potty trained. We put him in a pull up in the morning, and he'd be dry when we picked him up at night. We told his older sisters to help him, but they were only 5 themselves.. Lol I'm assuming the CM's helped him when he needed to go.