There’s no reason why you can’t talk with your son or daughter about everything they need to know.
You may have to do your homework about certain things if you're not sure of all the facts (periods or wet dreams for example).
Many single parents like to give their child the option of chatting to someone of the same sex. Ask trusted family members or family friends. It is best to agree together beforehand what you’re going to talk about and what your values are – this way your child won’t get different messages from different people.