The boys were crazy about the San Luis Obispo Children's Museum. I think we're going to have to get annual passes there.
They were also NUTS about the hotel spa! So nuts, in fact, that they've coerced us into getting one for our backyard :-)
Apart from the museum and the jacuzzi, we also had a blast visiting Morro Bay and Avila Beach. If you haven't spent time in SLO, you're missing out!