Major Dimakatso Mooi says the deceased cousins aged between three and seven-years old were found by their grandmother in an old freezer in the yard on Tuesday night.
Its believed the freezer accidentally locked while the children were playing inside it.
Police are appealing to parents and children guardians to take responsibility in ensuring their young children are safe at all times.
He added that yards should be cleared of old equipment and scrap that can cause harm to children.
A similar tragedy happened in Ermelo in 2014 when four children were also found dead inside a freezer.
Three boys and a girl, aged between four and seven were last seen playing outside.
