For the question above, we will use probability.
after 4 children, there is 37.5% chance you have 2 boys/2 girls
after 5 children, there is 62.5% chance you have at least 2boys/2 girls
after 6 children, there is 78% chance you have at least 2boys/2 girls
after 8 children, there is 93% chance you have at least 2boys/2 girls ...
based on this i would say a reasonable expectation would be about 6 children
I hope this answer helped you somehow.
