Children feel the number of transitions more than the number of sights
Adults often judge a day by how many places were visited, but children react more directly to waiting, hunger, uncertainty and repeated changes. Two full attractions in one day usually mean more packing up, more queueing and more shifting between vehicle and walking time. That can drain energy surprisingly fast.
One main attraction plus one light stop is usually the safest structure
This structure gives the day a clear focus while keeping enough energy for the most worthwhile part of the schedule. The lighter stop can be a short viewpoint, a simple walk, a snack break or a scenic roadside pause, rather than a second major visit with its own full logistics.
Lunch, toilets and afternoon mood should be planned before attraction density
Many family travel problems do not come from the attraction itself, but from moving the child into the next stage at the wrong moment. If lunch is late, toilet access is awkward or the hottest time of day is spent switching locations, the second stop usually becomes much harder to enjoy.
The exception is when both stops are highly convenient and the second one is very easy
If two places are truly on the same line and the second one requires little walking, little waiting and almost no mental reset, adding it can still work well. The real test is whether that second stop keeps the family rhythm intact rather than fragmenting it.