I would call. I think if it's a child young enough to sleep in the same bed as a parent, it doesn't count as a 5th person in the room. Can someone confirm that? I'm pretty sure 4 in a room means 4 adults, and there are some exceptions when there are parents with little kids involved. For example, a mom and a dad with kids who are 8, 6, and 5 wouldn't be forced to buy 2 rooms and split their family. However, if your kids were 18, 16, and 11, Disney would tell you you need either a suite, or two connecting rooms at a value resort. It will depend on the age of the children involved. Again, maybe someone else more knowledgeable can confirm what I'm saying, but I'm pretty sure that's the case.
If you're nervous about what they'll tell you, consider calling and acting like you're interested in a new reservation. Explain the situation in your family... for example, "I'm traveling with my husband and three young kids, and we want to stay at All-Star Sports. Do we have to book two rooms for our family? That would be a waste for us because we all stay in the room together."