Tom Thumb and Thumbelina are closely associated in pop culture, for obvious reasons. They've starred together in two direct-to-video movies. They appear as a couple in Shrek 2. I've also found mistaken statements that General Tom Thumb's wife used the stage name Thumbelina.
It's interesting to see how these crossovers treat the characters. The Adventures of Tom Thumb and Thumbelina was basically just a retelling of Thumbelina; despite getting first billing, Tom was barely the deuteragonist and bore no resemblance whatsoever to his original fairytale. Tom Thumb Meets Thumbelina seems like it took inspiration from both fairytales, but otherwise just kind of . . . does its own thing.
In a Nutshell, by Susan Price, is a fairly short book published in 1983. It can be a little hard to find in libraries. The main characters, Thumb and Thumbling, are a pair of tiny fairies who anger King Oberon. As punishment, he takes away their powers and gives them to human families. However, the tiny man and woman decide to find each other and get back to Fairyland - which is a tall order for a couple of people only two inches tall.
It's one of the most interesting mashup of thumbling tales I've read.
Though Thumb is (like Tom Thumb) based in England, and his parents use that name once, his adventures of riding in a horse's ear and being used to fetch stolen goods for robbers are all Thumbling. Thumbling, given to a lonely woman in Denmark, is Thumbelina, and the quest and conclusion are strongly based on The Young Giant.
The characters are unlikeable. They're supposed to be unlikeable, as fairies are played up as uncompassionate creatures, but it's still hard to get invested when they act as callous as they do. They only start to come around and grow into better people near the end. One touch I liked was how much we see the danger of their lives; Price does a pretty good job of making it feel like they are constantly threatened. Even their adopted parents could easily harm them, and overpower them by far.
I don't think this book is going to be remembered as a classic or anything like that, but it was an interesting read, and I have it on my bookshelf now.
This website is based on my research into folklore.