If you want to visit a temple, you could go to Man Mo Temple just west of Central.  It's centrally located and visually interesting, but not so big that the kids would get bored easily.  And if they did, you could easily shuttle them back outside.  It's also close to the area with all of the traditional Chinese medicine shops if they're the type to be interested in weird dried/bottle creepy crawlies.

The walk up to the Lantau Buddha isn't really that long, but it is a bit of a trip to get out there, so they might be a bit weary/bored before you even get there.  It might have come from living in East Asia, but I was underwhelmed by the world's largest outdoor seated bronze Buddha.  (Considering we've also seen the world's largest jade Buddha, the largest outdoor reclining Buddha, the largest stone Buddha built on top of a noodle shop, etc.  ...okay, maybe I made that last one up.)

If you're looking for an out of the way walk, you could take the ferry over to Cheung Chau (one of the outlying islands).  There's a cave at the tip of the island that's said to have been a pirate hideout.  It's a pleasant little walk, though the scenery isn't terribly impressive.  However, I was surprised how rural it felt in the little fishing villages out on the smaller islands.  It was quite a contrast to the ultra-modern bustle of downtown.

Take the kids to the Big Budda, you don't want to miss it.  I recommend a tour you can book at your hotel.  Lunch is included.  They do not eat meat, so tofu is used in it's place.  It is really good!  I had read before going, to be careful where you eat shrimp, and other seafood.  I left the delicious looking shrimp on my plate, only to find out later that it was tofu.mm I swear, it looked just like shrimp. Your tour guide will point out the "shacks?" over the water. They are worth a lot of money.  It is not that much walking...but I passed on climbing up the stairs on the Budda.  Kids are pretty resilient, especially, when they are climbing a golden Budda,  My daughter filled our days with things to do.l also investigated where we'd like to eat(Journeywoman.com).  We made reservations, in advance where we could.  We took Girl trips to the Panama Canal, Hong Kong, Ireland, and a 21 day trip. We took two cruise and Yukon territory by bus, we spent two days in Denali, took the all day bus tour (definitely recommend it) and my daughter did the river rafting trip.  If you plan to cruise to Alaska, be prepared to pay some big bucks for the tours.  If you just get on the ship not much to do our see, except in Juneau, and you could hang out at the bar in Skagway. Sorry, got off topic there

We live in Hong Kong with our 4 & 6 year olds. My kids have been to the Big Buddah a few times, but never walked up the steps. It's still worth the trip.

When we bring visitors out there we make a whole day of Lantau -- we take the MTR to Tung Chung, then the cable car to Ngong Ping (make sure you get tickets for the "Crystal" cabin -- costs a little extra, but usually a shorter line and it's a glass bottom car -- our kids LOVED it!), walk through the Ngong Ping tourist trap of a village, to the Big Buddah and then back to the monestary (gorgeous buildings some of which are being restored or built, not sure which). You can then grab a bus or taxi from Ngong Ping to Tai O -- a great little fishing village. Taxis are really hard to get in Tai O, so when you arrive check the bus schedule going towards Mui Wo (I think it's bus #1 and 11) so you know how much time you have to spend in Tai O. Usually 90 minutes is plenty time to walk all around the village and do a little boat ride through the village which then goes out to open water looking for Hong Kong's famous pink dolphins. We've done the boat trip probably 5 times or more, but only saw a dolphin once -- so don't get the kids hopes up too much.

Once you get the bus from Tai O, get off at Lower Chung Sha Beach. There's a famous beach side restaurant called The Stoep (pronounced "Stoop"), but we prefer a new place that serves only salad, pasta and pizza -- I forget the name, but if you walk past The Stoep and all the other restaurants, it's the last one. Amazingly fresh and delicious food. You can hang out on the deck or at one of the tables in the sand, have a drink and let the kids play around in the sand. Once you finish up there ask the restaurant to call you a taxi or go back up to the main road and take the bus to Mui Wo to catch the ferry back to Hong Kong. Here's a link to the ferry schedule. Try to get the fast ferry back, it's worth the price difference. http://www.nwff.com.hk/eng/fare_table/central-mui_wo/

As for other temples, my kids weren't at all impressed with Man Mo, but we've been a few times to the 10,000 Buddahs in Shatin and they love it each time because of all the different statues. We usually drive ourselves out there, but I bet there are buses available or the MTR goes to Shatin, although not sure how close it is to the temple. Here's a link: http://www.hongkongextras.com/_ten_thousand_buddhas_monastery.html

There are alot of steps to walk up, but it's a more gradual asecent compared to the Big Buddah, plus the kids are entertained by all the different faces of the buddahs along the path. And we've seen wild monkeys there, so keep an eye out (and don't bring food because they can be v. aggressive if they like what you have!)

You mentioned Duk Ling. We've not done that one, but there's another traditional junk called the Aqua Luna which we've done a few times. One was a half day trip which picked up in Central, went around the island to Stanley where we had time for lunch and then went back to Central. If you want to watch the light show, our favorite place to view it is from the Aqua Luna. It's the only option I know of being on the water to see both sides.

We were just at Top Deck on Sunday. You might want to call ahead and ask if they have a kids menu if that's all that your kids eat. I didn't see anything on the buffet line that was aimed just at kids. Mine loaded up on mussels, sushi, basmati, ribs, crab legs and corn on the cob. Just a warning about the "play area for kids" that they advertise -- it's a tiny room with padded floors, a puzzle or two and coloring books. Although they do have a sitter in there, your kids might be bored with it as mine were. You mentioned taking a sampan there. If you do that you might want to start from the Aberdeen Promenade because its a longer boat ride and the driver can take you through the fishing boats first then drop you at the Jumbo. Otherwise you can get a free shuttle boat (owned by the Jumbo and not a sampan) from the little pier near the Aberdeen Marina Club or I think they are also at Aberdeen Promenade.

Have fun!!