I think the 5 year old will be old enough to understand and remember the importance and history of it. The 3 year old will be antsy after a while (but you know that!). I would make sure you bring lots of snacks and coloring books to keep them busy. Maybe a new toy.
Looks like we may make it a family history lesson -- brother to bring his 3 1/2-yr-old. Lots of snacks neccesary for brother and kids, lots of tissues for me.