Our garden isn't huge so one of the things we've been trying to think about is incorporating things of different heights, and climbers. You could also look into vertical planting. That's down the line for us, but looks seriously interesting. We've also been painting the fence green, so once it's planted it'll be harder to see where the garden ends - theory is it makes you think it's larger than it is. We've got a 5 yr old and one of the things we're doing is creating a wigwag and will be growing hops over it. She gets a den and we get interesting greenery.
Now I feel silly. Maybe the OP can tell us what they did in the end.
I actually think tiny gardens can be the best gardens as you utilise each cm of space. I would create a few outdoor sitting areas to capitalise on light and then plant accordingly with some large specimen plants. How about some large hardy palms, Phormium and Schefflera?
I had a large country garden, now I have a tiny one , surrounded by a 6 ft fence. I always thought it would be easier to have a courtyard garden, but now I have one, I find choosing plants difficult, as there is nowhere to put my mistakes!
Hi Lois Lane, Hope you have had some good ideas from all the above responses. I would be inclined to pave part of the garden with some light coloured non-slip paving, and have an area with rubber chips/bark/artificial turf for the playground area. Build some raised beds for plants so that trike wheels do not run over the flowers and have lots of climbing plants on the fence. If you invest in folding garden furniture it will be easy to move out of the way for trike riding. Good luck and have fun!