The little boy protagonists in Judith Viorst's other books are Alexander's brothers.
The five-year-old narrator of I'll Fix Anthony is Nick, before Alexander was born (this is probably canon, and the live-action short film adaptation makes it explicit), while the protagonist of The Tenth Good Thing About Barney is Anthony, before either of the younger two brothers were born.Nina, Kelly's boss, and Ms. Suggs, the driving test supervisor, are mother and daughter.
Since they're both women in mood with attitude, who suck at their jobs, have a rough relationship with each other, dream of retiring one day, and maybe going somewhere where they won't be bothered, like Jamaica or Timbuktu.