Chicka Chicka Boom Boom by Bill Martin, Jr. and John Archambault, illustrated by Lois Ehlert

Chicka Chicka Boom Boom is another book that Luke really enjoys. It's about a bunch of lower case letters that all climb up a coconut tree so it falls down and all the letters fall on the ground. Then, the upper case letters come running to pick up the little letters. The illustrations are very simple and fun to look at.