In Budapest, celebrating summer is at the Vajdahunyad Vár. The Castle of Vajdahunyad. Of course, many families with small children will bring their kids to the Budapest Zoo, Funfair Carnival, Margaret island etc.
Vajdahunyad Castle, or Vajdahunyad vára, is a castle in City Park, that was built between 1896 and 1908, designed by Ignác Alpár. It is a copy in part of a castle in Transylvania, Romania, that is also called Vajdahunyad, though it is also a display of different architectural styles. Originally it was made from cardboard and wood for the millennial exhibition in 1896 but it became so popular that it was rebuilt from stone and brick. Today it houses the Agricultural Museum.
Some summer activities at the pond, you can easily rent a row boat and enjoy some romantic times if you are a couple.