The trick to a good family weekend is the same as any weekend: less ambition, more proximity. A 15-minute walk is a lower bar than a 45-minute drive, and you'll do the walk twice as often.
One booking, one backup
Book one thing ahead — a parent-and-kid pottery class, a junior bouldering session, a Saturday swim — and hold one backup in your back pocket for rain. Everything else, improvise.
Keep the same Saturday
Kids love repetition more than variety. A "Saturday routine" — same park, same café, same class — is cheaper, calmer and quietly becomes the part of the week everyone looks forward to.