You are looking at at least 2 hours by toll motorway.
If you take the scenic coastal route via Troia, Vila Nova Milfontes, Aljezur, Lagos allow 2 hrs. 30 mins depending on time of year.
In Lisbon there are great things for kids such as the massive walk through Aquarium at Parque de Nações, the Zoo at Sete Rios, Tram Rides, the train ride along the Coast to Cascais, Toys R Us in the Colombo Centre, the kiddies park with rides etc. also in Colombo Centre.
All accessible by Fertagus train and Metro from Setubal station over the 25 Abril bridge and into Lisbon.
