I tried to fix my spot in the middle of my backyard here in Arizona. We dont use playground.
I tried different seeds and aeration fertilizer...
Adjusting the sprinkler heads, watering etc.
What else I can do?
You are 2000 miles from me.
This is probably Bermuda grass. Warm spring weather is the time to help the Bermuda spread.
For instance take plugs from other parts of the lawn and plant them in the bare area. A grid with plugs 4 to 6 inches apart should work.
But maybe someone close to your location has more experience.
Find the cause of the bare spot--correct that--first.
Bermuda wants sunlight, 1" water a week, and lots of N. Keep little ones off the grass if you want it to spread, at least until its established, and after that it will need more attention than the rest of the lawn with more N and more frequently. A soil test is recommended in that bare area, I'm betting you have alkaline soil with poor nutrient uptake for the grass.
You will need to drop seed, topdress with good soil, fertilize with a starter fert, water heavy the first few weeks, and keep kids off it. Otherwise fill it with sand and gravel and let them run and play on that.
It would be better to do this as soon as it greens up next spring than try it now.