Perhaps it is time to put a spoiler warning, for those who didn't read all the Harry Potter books available so far.

>>So far, my son (12 years) has been resisting this sort of magic, but my daughter (14 years) has read all the Harry Potter books so far, and (just like me), is impatient to read the last one.
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>Are you sure there will be more? I'd love to contunue to read, but in the last book Dumblerdof (? spell) was killed... :(

Professor Dumbledore (Albus Percival Wulfric Brian Dumbledore)

It seems quite obvious that in the seventh year, Harry will continue his fight against Voldemort, with whatever help he can obtain from his two best friends, Prof. Dumbledore's image, many other friends, and probably help from some unexpected sources.

The seventh book will be the last one in the series, according to the author, although she might write some "school books" (did you read "Quidditch Through the Ages", and "Fantastic Beasts and Where to Find Them"?).

More information in the Harry Potter Lexicon: http://www.hp-lexicon.org/about/books/book_6-7.html