When the Pigeons Arrive(1968)

Original title: Kad golubovi dolete

A group of children build a loft in an abandoned yard, but instead of pigeons, a man and his two sons move into it. At first, boys try to get rid of the unwanted intruders, but eventually they befriend with them. However, the municipality sends their men to tear down the illegal housing, but the children decide to stop them at all costs.