A few thoughts about my screw-terminal design pictured earlier: it’s simple, but I think the reality is that most wires are going to be fairly direct inside a toy, and it is unlikely you’d have the slack to just snip a power wire, strip the ends, and route both to a convenient location for the jack, so you’d end up with two wires spliced in. So I’m changing direction (though if the screw terminal design appeals to you, I have the PCBs, and the parts are just DigiKey).
With the same goal of making this a solderless adaptor, let’s just solder some 18 AWG wire (6-12" long) to a 3.5mm jack and provide 2 Wago 2-position lever nuts. Heat shrink for strain relief at the jack. Color code the wires red and black just for fun. Supply an optional inexpensive wire stripper (18-28 awg?). (I’d lean a little towards the ultra-flexible silicone rubber insulated wire.)
Another issue is the thickness of plastic enclosures. It’s not unusual for the wall thickness of toys to be over the 0.07" or so the typical 3.5mm rear-mount panel jack can accommodate. So think about using a front-mount jack (example: https://www.mouser.com/ProductDetail/Switchcraft/35FM3AU?qs=u16ybLDytRbvaaTyauyb0g%3D%3D, though this one is very expensive). There’s no problem with the wires passing through the hole from the outside–just don’t put the Wago’s on until after you insert the wires through the hole. Or, there are some rear-mount that go to 3mm thick (0.118") like: https://www.maykrshop.com/product/3-5mm-stereo-audio-jack-panel-mount/ I haven’t done more than a quick search, so better ones are probably out there.
The only downside that comes to mind is that Wago’s have a little mass, so they’d bounce around if not secured with a twist-tie or hot glue. A soldered joint with heat shrink isn’t going to do that. I think the tradeoff of not required soldering skills may be worth for some cases.