It was phenomenal and free, so that is always good. The climb might be rough for little ones, but I do think there is a lot higher up. I hope you have a blast! I still have a lot to cover from our trip.
They'll be 6 and 4. My 4-year-old will climb until he’s worn out, then he can ride on my shoulders. My 6-year-old, on the other hand, seems to have endless energy. On some of my longer run he will ride his bike up and down the hills with me the whole time.
Sounds like the are good to go then! The altitude difference is the only thing I would be worried about at that point.