Tuscany for a week + 3 days?

Hi We are a large family, 7 adults and 4 kids, planning to rent a villa near Florence for a week. We will do Florence, Siena and Pisa from there as day trips. We are landing in Milan and plan to drive from there and back.
We wanted to spend 3 days before the villa somewhere near Milan where the kids will have fun (aged 4 - 12). What would be the best place in driving distance from Milan? Lake Como, Switzerland or some other place? Thanks Pradeep