Sadly, I did this (wasn’t even the kids) when trying to put it together.. I found nothing online for a fix. I took apart the screws on the base piece. There are 2 on the outside and a few on the inside. This allows you to take out the periscope and the piece its attached to.
There are two screws on the bottom of this piece (red). After taking these two screws out you can see why you couldn’t pull it apart!!! At this point, I tried with screw drivers pulling at the tabs (two at a time), although they were tough, one eventually did break. The piece was then able to be pulled/pushed out and came undone. I was able to reassemble it properly and it all works without issue. I’m sure there is a way to get it out without breaking it, but no luck for me.
Hope it helps