Any book suggestions for DS (9yrs) and dd (11yrs) ?

[JaneZane]

Both are good/able readers.

DS (9yrs)loved:
Diamond brother series by Anthony Horowitz (but didn't much like Alex Ryder series)
Percy Jackson series
Wimpy kid and Tom Gates (although they are too easy now - he still re-reads them though)

Dd (11yrs) loved:
Wonder by RJ Palacio (think this has been read multiple times!)
Harry Potter (all)
Lady Grace mysteries
Percy Jackson Series
Cath Cassidy
Lemony Snicket (all)

I want some challenging but fun books for them both. Any suggestions?
Thanks

[SecretSpi]

Michelle Lovric's The Undrowned Child and following books for the 11 year old - they are set in Venice.

Has your son read the Charlie Bone books by Jenny Nimmo yet? May interest him if he likes series.

[PomBearWithAnOFRS]

Anything and everything by Susan Cooper - not just her "Dark is Rising" series (and ignore that vile heinously bad film they made of it, the books are wonderful!)
Ingo and The Tide Knot are good, and the "Connie Companion" quartet, but I've forgotten who wrote them both

[Booksteensmagazines]

Ingo is Helen Dunmore I think

[kimlo]

Not particularly challenging but dd1 has been racing through the babysitters club. Shes reading 2 a week and shes loving them.

Theres over 100 of them and they are all available on kindle.