If you're looking for graphic novels, my 7 year old daughter really liked Zita the Spacegirl by Ben Hatke. Actually I liked it too, it was fun to read together. There's three books in the series, it's a great story.
Zita, the Space Girl
https://www.amazon.com/Zita-Spacegirl-Ben-Hatke/dp/1596434465
definitely for small children