As someone who spends far too much time every summer in maintaining an above-ground pool, take my advice.
For a small pool like this, just empty it. You can use the water for watering your plants.
If you have left it for a few days, clean it with a brush and washing-up liquid to remove the algae and all the other nasty stuff that will be present. Rinse it a few times to remove all of the detergent.
MOVE IT - to a new location. If it has only been covering a patch of grass for a few days, the grass will recover pretty quickly. I now have a permanent spot for the pool, but before I did this, I used to have TWO pools and keep moving the empty one around the garden and pumping the water from one to the other.
Refill it with lovely fresh, clean water. This is FAR easier than using chemicals, pumps, filters and covers to keep it clean. Take it from me. None of that stuff is cheap, if you calculate how much it will cost you to refill it every day for a whole season, my guess is you won't save any money by treating it like a proper pool.
This may not be a very PC thing to say but it may also be worthwhile just throwing away the pool at the end of the season rather than clean it. You will never get it as clean as a new one and you will spend time, energy, water and detergent trying to achieve it. They are not very expensive so it is likely to be more sensible to get a new one, if, indeed, your kids are still interested next year.
Final tip: if you do throw it away, consider buying the next one during the off-season when they are cheaper.