Kumharas at Cala de Bou (south end of San Antonio Bay, near to Port Des Torrent) is a very cool chill out place for sunsets, right on the beach. Have seen families there loads of times. Very laid back, plenty of space, not as commercial as Cafe Del Mar and the rest of sunset strip. Having said that, have seen kids at CDM too, but a five year old may find the crowds a little overwhelming.