I Am Too Absolutely Small for School 

"The children's relationship is refreshingly noncombative, with Charlie as the protective and affectionate older brother who is appreciative of, rather than annoyed by, his sister's quirkiness." - SCHOOL LIBRARY JOURNAL (starred review)

Lola is not so sure about school. After all, why would she need to count higher than ten when she never eats more that ten cookies at a time? Once again, it's up to ever-patient big brother Charlie to persuade Lola that school is worthwhile — and that her invisible friend, Soren Lorensen, will be welcome, too.