Edit: "Children of the Dog Star" (NZ 1984) aired in Britain in August '85. It features children in a rural setting, it's scifi and something in a swamp with a hole in the middle is recovered. Below is the recovery from the swamp and assorted mystery devices:

![enter image description here][1]
![enter image description here][2]

Source: http://www.frequency.com/video/children-of-dog-star-1984/101862698/-/5-6263323




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It could have been a re-run of "Here Come the Double Deckers" from 1970-71. It takes place in a junk yard in London where a group of children live in an abandoned double-decker bus. It features a fair bit of tinkering and a robot in at least one episode. It was a joint UK-US production, which might explain the accents you remember. It was a deliberate attempt at creating something along the lines of "Our Gang"/"The Little Rascals".


![enter image description here][3]
![enter image description here][4]
![enter image description here][5]
![enter image description here][6]


What the writers tried to emulate:

![enter image description here][7]


  [1]: https://i.sstatic.net/RHOvJ.jpg
  [2]: https://i.sstatic.net/SVUXX.png
  [3]: https://i.sstatic.net/xAzpr.png
  [4]: https://i.sstatic.net/gwpue.jpg
  [5]: https://i.sstatic.net/ThHjW.jpg
  [6]: https://i.sstatic.net/RBHIp.jpg
  [7]: https://i.sstatic.net/IHL7l.jpg