Charles Stross's Merchant Princes is a rolicking good read, and well suited for teens and near I think - our eldest loved them. I recommend the first six (the six books are now sold as a trilogy, as they were originally intended to be).

The relaunch of the series with a new follow-up trilogy rather loses the plot and was a big disappointment... So I'd stick to the originals. :)

https://en.wikipedia.org/wiki/The_Merchant_Princes

Jonathan Stroud's award winning Bartimaeus Trilogy (in 4 parts with prequel) is younger - probably around 8 or 10, and is one of those children's series that there's a good chance parents will enjoy too. More alternate history and fantasy than sci-fi though. There's an adult layer in things, and a deliciously acerbic and sarcastic main character, so a good series for reading to them. I think I would have bought the rest of the series even if the kids hadn't enjoyed the first! Hugely recommended.

His other series, Lockwood, is similar but perhaps less for the adults though there's similar humour. They're a group of kids who are ghost hunters. So more squarely in the Harry Potter vein.

Younger still and I draw a blank, sorry - it's been a good while since our kids were in that age bracket. If I do remember anything suitable I'll update.

https://en.wikipedia.org/wiki/Bartimaeus_Sequence

i pretty much enjoy any book that Stross publishes, including the merchant princes series, but things do get rather grim. (now kids, what do you think would _really_ happen if a superpower discovered a doorway into narnia? ...)

You can find award winning books of different genre in the database of award winning children's books: http://www.dawcl.com/

You can browse through winners of the Carnegie Medal here: https://www.carnegiegreenaway.org.uk/archive.php

Weirdly they don't keep the short lists. :-/

EDIT: here are the shortlists for a few years. You can find them easily with google:

https://www.carnegiegreenaway.org.uk/press.php?release=pres_...

https://www.carnegiegreenaway.org.uk/press.php?release=pres_...

https://www.theguardian.com/childrens-books-site/2015/mar/17...

http://booksforkeeps.co.uk/childrens-books/news/2012-cilip-c...

I.e. I have read Hitchikers Guide to the Galaxy as ~13 year old and enjoyed it immensly. Terry Prattchets later discworld books might count as well, i.e. Going Postal, Making Money and Raising Steam is quite a bit about new technology and its influence on the changing world :-)

Ah, now I see, 3 to 6 year olds.

My daughter is 5, and we haven't really been reading sci-fy, but next time I might ask in our library :-) We mostly read fairy tales an light fantasy (i.e. she really enjoyed Hilda)

But she likes machines and robots and I amused her several times with i.e. guides through International Space Station or documentaries about various robots on Mars :)

"Escape to Witch Mountain" (by Alexander Key) is a classic.

edit: aside from scifi, garth nix' "sabriel" books are a pretty good read. fantasy, necromancy, & quite an imaginative take on how magic systems work

What if? is more speculative of the two, and you can read a few of the stories/speculations on https://what-if.xkcd.com/ :-)