Which of these two sentences do you think is the correct one?
He has got three children, two daughters, one son
He has got three children: two daughters and one son.
Thank you for you help
A colon is perfectly correct here. In fact, this is an example of one of the most common uses of the colon - the opening clause establishes a set, the text following the colon lists the elements of that set. The dash is often used instead of a colon but it's simply a question of preference.