First decide whether the seniors are bored or genuinely tired
These are not the same problem. Sometimes older travellers are simply less interested in the current stop. Other times their legs, back or energy are clearly fading. The second case should not be tested with one more stop just because the rest of the group is willing.
Children still having energy does not automatically mean another formal sight is needed
Many children mainly need a lighter space to move, snack and reset. That can be easier to provide near the hotel or around dinner than by adding one more structured scenic stop with entry, walking and return timing.
An earlier hotel return often improves both the evening and the next morning
When hotel arrival slips too late, seniors recover less well and children's bedtime gets compressed. If the next day also starts early, one extra stop in the afternoon can reduce the whole group's efficiency the following morning.
Only keep the small stop when all three conditions are true
It should be directly on the route, require only a short stay, and still allow a calm dinner and check-in afterward. If any one of those conditions fails, closing the day earlier is usually the stronger call.