Don't use air b&b it's destroying the city. There are plenty of hotels/b&b/hostels.
It's not a car city. Look for places on the tram route as the DCs might enjoy that.
Edinburgh is a city for hearty walkers- it is very very hilly with lots of alleyways with steep steps. Make sure dc have a lot of stamina before going!
For DCs the best bits are probably:
Zoo (another huge hill)
Our dynamic earth
Camera obscura (near castle)
Museum of childhood (down the royal mile from the castle)
National museum
Open top bus tour
Going up the Scott monument
As above the castle isn't that interesting for DCs.
Go to grassmarket for an ice cream (there's a shop with a permanent queue.) opposite there's a cat cafe. From here there's a good view of the castle.
Holyrood is worth a tour.
There aren't many playgrounds in the city centre you have to go to the meadows.
If they like beaches I'd choose south queensferry over portobello as the view of the three bridges is spectacular and you can do boat trips from there.
If you like walks there's the water of leith walkway, Arthur's seat, calton hill, the botanic gardens or one of the many ghost tours if your dc like that kind of thing.
Then there's the usual stuff in most cities- dungeon, cinema/bowling, shopping.
If they like HP unfortunately the cafe where JK wrote it had a bad fire and afaik hasn't reopened yet.