Yeah, I was soldering little kits at a pretty young age. With proper supervision it feels you might as well have the kid really go for it, or have them direct the parent and lead them through the soldering process, while the parent performs the actual connection, showing proper technique and safety, including ventilation etc.
Soldering would make the toy permanent into whatever configuration it was soldered into. This allows for undoing, redoing, rinse, lather, repeat. That's what makes it fun. You do it once and use solder, you learn that you can follow directions and work a soldering iron. These type of "toys" can lead to experimenting by undoing, and then connecting to something else.
I can't see when I'd find an hour or two undisturbed to learn to solder! And it's not something you want to be doing with younger kids around necessarily - even though the older of your children might be old enough to learn to solder, you may still be looking after younger children. Even with something as simple as getting out all the painting stuff, I have to be the right frame of mind to be able to cope with the chaos and mess!
