This is a good transition by Medina, who has both picture books and young adult novels to her credit. There are a lot of topics being covered, which makes this book a bit on the long side, but her feel for middle grade emotions and reactions is on point.
Mental diminution in the elderly is a topic that young readers should have some knowledge of, since many of them will face problems with their grandparents before they are too much older. It always surprises me that families don't expect or discuss After my mother was diagnosed with Parkinsons a dozen years ago, we told the girls exactly what to expect. My mother is doing fairly well for 84, but none of us are surprised when she is confused. I guess it makes a better story the other way, since almost all books dealing with grandparents and dementia react with denial.