It depends on how little they are and how much stamina they have. It’s not that far but it has many stairs. You should definitely not be in a hurry. If they are good walkers they can do it, but under about 3 yrs I would suggest you should be prepared to carry them for short stretches. Also, think about how to motivate them: counting steps, singing songs, looking for bugs, regular pauses and rest, promise of a small candy at mid-point and top, things like that. I think they will be impressed with the buddha, and feel very proud of themselves when they reach the top. An alternative is to do only the boat ride in front of the buddha, not tiring at all and still a good view. Have fun!