It's useful to go to a country which has a lot of English-speakers (not expats, but in a country where a lot of people will try, or will, learn English, for jobs etc; and in schools). For instance, Sweden, where I've found (I was born there, but this is DH's experience really, not mine) a lot of people will speak at least limited English, and a lot of TV shows are ones converted into that language from English, and quite a few businesses will actually have things in English (I don't know why though?).
I thought electronics engineer was good enough for a visa, according to this so where did you find out it wasn't? It appears to be up to date information, and from ANZSCO? Might be wrong of course!
Otherwise, Switzerland sounds good. If he already worked there for a few years, he has a good-ish understanding of life there, and has a bit of knowledge about daily life, not just holidaying there. If you can speak French well enough, it's good, although I would advise you to start simple German lessons (a large part of Switzerland speak German, as well as other languages too, as you probably know) just to make sure.
Like natation says, under about eight they should be fine, over that, it will take a lot of work (for instance, as many French only DVDs as you can find, especially ones which are French versions of English language films, mostly French books, and making sure you speak to them in French as much as possible is obvious, loads of stuff- if you want some information before deciding, check over on Bilingualism).