Billy's Clubhouse (Knopf, 1955) written and illustrated by Marion Holland

Billy (from Billy Had a System) and his friends hang out at a nearby vacant lot. For years, it's been their spot. Just when they've fixed up a new baseball diamond on the lot, a realtor comes along and puts up a "for sale" sign.
In Billy's Clubhouse, the gang tries to save the field.
In Billy's Clubhouse, the gang tries to save the field.