Heck even without kids we book far in advance, but that is because the types of vacations we book at present are a combo of popular place, crazy popular time, and small number of spots available. Relevant example, the only
DCL cruise I have booked right now is the 8 night to Bermuda on the Fantasy next year. If we wanted that one, we had one choice. Over Christmas we're back on the Letty for another week with the Galapagos, sold out with only 20 available spots. NEXT Christmas we wanted a Danube Christmas Market cruise. Probably not sold out, but we got the week we needed in the cabin category we wanted by booking almost two years in advance. Any later and it would have been sold out like this year is. If we didn't care exactly when or what company we sailed with, I'm sure we could have thrown something together, but that's not how we choose to spend vacation dollars on the big trips.
The language says "We continue to strongly recommend unvaccinated guests wear a face covering in all indoor locations" under 'Youth Activities' here
https://disneycruise.disney.go.com/why-cruise-disney/experience-updates/on-the-ship-us/. Going by this this is not a requirement, but a strong suggestion.