Our first cruise was 3 day on the Dream there were 1500 kids on the cruise. The clubs were packed. My daughter (6 at the time) went a few times. The first time she went for a specific activity and had a good time.
The next time we left her was in the evening when I went to get her I found her propped up on a chair dozing. Other kids had been given mats and it seemed to me, her mom, that she was being a little neglected

. I didn't get why one of the CM's didn't lead her to mat to lie down.
The third and last time was on
Castaway Cay. We dropped her off and the kids were at lunch she was told to go sit and wait for everyone to be finished. She looked so sad I felt like I had left her in prison. We came back about 15 minutes later to get her and they were still sitting at the lunch area. She saw us and came running. One of the CM's yelled at her in a really harsh tone to sit back down, she is very sensitive and broke into tears. The CM quickly apologized, I think she knew that she had been a bit harsh. It took forever to get her out, but there was no way they were going to let her out without going through the security measures.
We were not at all impressed with the kids clubs I did feel that they are presented as more supervision than they really are, and I definitely don't think that Disney can do no wrong.
On our second cruise on the Fantasy we had a much better experience. My daughter was refusing to go to the clubs before we got on the ship. She made a friend and was much happier at the clubs with her friend. I think there were a number of reason why it went better the second time. Less kids, a longer cruise, and our expectations were more realistic with regards to the club.
I do think the clubs are a safe place for kids. I might keep a younger child out of the club if I had a concern, but if your kids go to school and play in a school yard at lunch they are prepared for the clubs. Based on our experience I have a hard time seeing how a child could leave the club unnoticed.
Based on the fact this incident was on a 4 day cruise, I would think the experience in the clubs for this Dad would have been more like our first cruise. I bit chaotic in the clubs and difficult to track the location of ever single child. I really don't understand why he felt like the gangplank was the first place look but different people with different perspectives.
If he had just stopped and and took a deep breathe he could have saved himself and his wife some heartache.