Well or Cistern

I found a well or cistern under a few feet of dirt in my backyard. It was capped with a slate slab (maybe an old sidewalk panel). It’s about 5 feet across at the top, 8 feet across at the bottom, and maybe 10 feet deep. It’s lined with brick throughout and looks to be in good shape. I haven’t been down to the bottom yet but may see if anything interesting is there. My question is what to do with it. Is it best to fill it in and recap it? If so, I have the tons of dirt I’ve been digging up (including many sandbags full) but dirt may take time to settle. I have a young child so can’t leave it open. If anyone has been through this, advice appreciated. Thanks.