My brother *loved* reading dictionaries when he was about that age. (I didn't understand him then, either.) He started with The Cat In The Hat Spanish-English/English-Spanish Dictionary which you may be able to find in the library. It's sort of a cross between an alphabet book and a phrasebook for young travelers who find themselves in foreign kindergartens, zoos, etc. There was a very similar one for French. He liked a German dictionary that was written for children, but not such young children...maybe 8-10? It looked more or less like a dictionary, but the font was like a regular book, the definitions were simple, and there were a lot of pictures. For Greek, he wanted a dictionary, but my father gave him alphabet books instead, and that turned out to be good enough.