If you are looking for a series for your second grade son (or something along those lines), look no farther than the Astrosaurs. I received a Cybils review copy of Astrosaurs--the Twist of Time, by Steve Cole (of Z-Rex fame), the 17th (I think) in the series, and (very happily) now have a nice long list of books to buy for my own second-grade son!
The Astrosaurs are herbisaurs who live out in the Jurassic quadrant of distant space. Their vegetarian sector abuts that of the carnivores--and the brave astrosaurs, a quartet of dinos led by the intrepid Captain Teggs, are constantly running up against the ferocious meat-eaters. This particular book involves a pool of time water on a distant planet--water that makes anyone (or just about anything) that comes into contact with it become younger and younger.... A vicious Allosaur thinks this could be the Ultimate Weapon...and will use it to seize control of the whole sector, unless Teggs and crew can stop him in time!
When I read this to myself, it was clear to me that I'm not the intended audience. For instance, a bucket of baby dino pee used as a weapon doesn't do much for me, although I want to make it clear that the writing was just fine and the story nicely coherent and not uninteresting. But still, not a book for people much older than nine or so.
But then I put it in the hands of my seven year old...and prised it out of his hands again at bedtime, and when he woke up the next morning, the first thing he said to me was, "Where's my book?" And I could hear him downstairs on the sofa, reading away with gasps and cheers...until he reached the end, and asked for more Astrosaur books! So, based on my (admittedly small) sample, these books have great appeal for the intended audience.
It's a UK series, but thanks to the Book Depository, they are easy to get a hold of. There's a companion series as well, Astrosaur Academy. And as an added bonus, the books come with character cards, which my boy appreciated. He's also intrigued by another series from the same author--Cows in Action.... There's lots of information about all these books here at Steve Cole's website. (By the way, I have a link to the Book Depository at right; any commissions earned help my local public library).