My brother's child who is six years old, keeps asking his mother for a baby brother to play with, What can she do or say?

That is an interesting question that I would ideally like to get the comments of other members.

A 6 year old boy is old enough to understand cause and effect. Does he want a younger brother because he has no one to play with or is it just a wish? Do the parents ever plan to have another child?

If the difficulty is in explaining the way babies, in this case younger brothers, are made, then it is worth them telling him the story about the bees. A simple way to go about it would be to say something like;

"Babies are made when dad's eggs and mum's eggs join together. This happens through a process that people get to know when they are grown. When the eggs have joined together, then the baby starts growing in mother's tummy and this takes about 9 months. After this period, the baby is grown and is removed by the doctor in the hospital". The amount of details you provide will be determined by his questioning.

What do other members advise?