I have done a load of cycling with my kids on their bikes, and me on my 20 inch BMX.
The longest ride has been 15 miles with the 7yr old, which was plenty, several 10 miles for the 5 yr olds, and a few 5s on my own round the MTB trail in the Olympic park.
10" bars are more trendy than laughable these days (even with a top load stem). And if you want to do tricks then short chainstays are your friend.
Cruising, posing and errand running are all fair game, it makes a BMX feel more 'functional'. If I had to only have one bike, it'd be the BMX.