CosmoCaixa (Science Museum) is not one of the main tourist attractions in Barcelona, it is more popular with local people. At the same time, there are also tourists who visit it. Since the museum focuses mainly on children – there are a lot of interactive attractions for them, and therefore it is visited by many families with kids.
Moreover, children younger than 16 years do not need to pay (for additional information – Barcelona for Free) and tickets are very cheap (4 Euros, as of 2017). CosmoCaixa is a good option if you want to spend a lovely, yet not too expensive, activity that kids would enjoy (for additional information – Kids and Families in Barcelona).
The only disadvantage of the museum is that it is a bit far from the city. If you would like to visit it with your family or with a group, it is recommended to get there by a taxi. In case of many persons a taxi is much more expensive than the metro and it is more convenient (for additional information – Public Transportation in Barcelona).