With kids, give Florentine Aperitivo (Santo Spirito / Sant'Ambrogio) a miss.
Aperitivo — the negroni was reputedly invented here — is the warm, social heart of a Florentine evening, and a piazza spritz at sunset is a perfect cheap pleasure if you pick a local spot. The catch: central squares overcharge for watered drinks and stingy nibbles, so the experience swings entirely on where you sit. Choose well and it's the most pleasant €10 you'll spend.