Personally I think that garden style is fine. Kids learn steps etc quickly and they aren't that steep
It's fine to add a sandpit in corner, have picnic in another, and to take toy dinosaurs outside for a play. Plus can fill baby bath with water in summer etc.
Rarely to people have a big enough garden to actually play. I think it's fine to have a garden they can go outside in and play with toys etc, and use parks/ commons/ fields to actually run and play
We live in Central London. We have a roof terrace. It's decked with fake grass in section. Has table and chairs, BBQ, sandpit, etc.
They are 3 and 4 and spend ages outside in summer on roof. They have a large pavement Slab each for chalking pictures, play in sandpit, have tea parties on a blanket, paint at table, take cars/ duplo/ animals etc outside, make dens with sheets/ pens over the table etc.
Every day we also go to the parks to run/ climbing walls to climb/ tennis on courts/ climb trees etc. Things even with grassy garden we couldn't have space for