it's obviously a wonderful historic stop, so maybe talk about the events of the day before you go, so they can understand the significance of the site.
That said, if they are super sensitive kids, the fact that so many men were lost there, and entombed there, might be really bothersome for them. It's emotional for most adults. The film before the boat to the Arizona has actual footage from that day, some of it not pretty (I recall a dead Japanese soldier in one snip), though your 7 year old might not even catch on that it's real footage. When you get to the Arizona you're expected to show reverence - not silence - but respect. There usually is a ranger there to talk to, but again, they don't sugar coat any of it, so your kids might find some of that disturbing. It was a brutal attack and it's not helpful for any of us to water it down.
Mostly though, the memorial park area is a lot of walking around, looking at plaques, reading historical info. My kids would have found it ridiculously boring at age 7.