Should you ever find yourself in Lisbon with a free afternoon to spend, I would like to recommend, from all my heart, the Oceanario de Lisboa.
It is a great place for families, introduce your kids to a lot of wonderfull species of fish as well as other animals, and encourage them to participate in the activities provided.
You can find more info on their website, as well as purchase tickets (I believe there was a 10% discount when buying online).
Have you ever visited the Oceanario?
Would you like to visit?