Posted: 28/10/2017 at 19:32
Just one thought - decking areas where you have the shade of trees won't be very good for a play area. Slippy as h*ll.
Anyway, apart from that! Can't see the pic clearly enough to ID your trees, but there are trees which don't cast heavy shade, and that would make them more suitable for your purpose. Many of the birches (Betula) have a light canopy, and some have beautiful, ornamental bark, so they look good for a long period. Amelanchier lamarkii is also an excellent tree/shrub. It doesn't get too big, and has flowers in spring, berries in autumn, and great autumn colour. Again, a light canopy, so doesn't cast too much shade. Some of the crab apples, or apple trees on dwarf rootstocks, don't get too big either, but it really depends on exactly how much space you have. They will all take quite a while to get big anyway.
If trees eventually get a bit big, you can always raise the canopy of them - that just means removing lower branches so that the 'top' of the tree is high, and you have more trunk exposed, allowing more light in.
Growing trees in pots can be done, but they will require a lot of looking after, so I wouldn't recommend it. Far better to grow something in the ground suitable for the purpose.
Planting in the ground is infinitely better for the trees, but when you plant, clear a good area round the base - about a metre in diameter. Grass will just compete for moisture and nutrients, and make it difficult to keep the grass tidy round the trees too. Prep the ground well with plenty of good compost and slow release fertiliser like blood, fish and bone, and once planted, and well watered in, apply a mulch of bark or something similar to help retain moisture, and keep well watered untill established, especially throughout the first year. Also - make sure they're properly staked.