Right. I just wanted to emphasize this point. Sometimes lighter people do get stuck. It's not a safety issue, and they fix is pretty quickly, but it does hold up the line a bit. Since you mentioned that they were both young, the main thing is to be aware it happens sometimes and for them to stay calm if they do get stuck.
When we were there there was this one boy (probably more like 10, not 7) who got stuck more than once. Eventually they asked him to ride with someone else in his group to keep from getting stuck.
Also, one thing they do when the wind picks up is switch to double riders only. This happened for entire day at sea when we were there, so if your plans for the aqua-duck include some kids that plan to ride alone, keep in mind that might not be an option all the time, and have a backup plan ready.