statistics using statcrunch

A married couple plans to have 4 children and are wondering how many would be boys. Assume there are no twins or multiple births and that the probability for having a boy would be 0.50. Is this a binomial experiment? Explain why this is a binomial experiment and check all four required conditions.

In the problem above you were told to assume none would be twins. Why? Which conditions for binomial experiment would be violated if they were twins