Re: Children's scifi and fantasy: an appeal to your collective memory
I did some more searching and came across the Pentagram series by Anthony Horowitz. I can't be sure they are the books of my second question, but the descriptions and publishing dates are promising. And they have been translated into Dutch.
Now all I want is to warn earth: watch Farscape... and share the wonders I've seen.
It's Tolkien, not Tolkein.