In The Witches, we see two examples of a family: our narrator and his grandma, and Bruno Jenkins and his parents. What we learn from this book is that having a mom and a dad, the typical nuclear family, isn't always the best setup. Bruno is pretty much ignored by his parents, as opposed to our narrator, whose grandma is very attentive and always concerned about him. Then, when both boys get turned into mice, Grandmamma is super-understanding, while Mr and Mrs Jenkins kind of go nuts. What defines a family is unconditional love. Loving someone even though they're a mouse is certainly unconditional.
It's great that our narrator loves his grandma, but he really should have some friends his own age. Family can't provide everything.
Grandmamma should have gone to greater lengths to protect her grandson.