I think they are anticipating the upcoming Alaska season on millennium, when there will be more children.
Most families are very respectful of the hours posted. Yes there is the occasional scofflaw, but a word to security or an officer generally takes care of it quickly
Should you happen to see someone in violation of the rules, remember that the crew who are setting out towels and cleaning up the area are really not there to enforce the rules, but they can quickly summon someone who has the needed authority.
to the OP, in general, children and Celebrity are not a problem. And by 5 o’clock, most adults are off having their pre-dinner cocktails, or dressing for the evening, and the pool wouldn’t be in use for that time anyway. If that is your preferred time to swim, I wouldn’t really worry about children interfering with your enjoyment of the solarium