Option 1:
Private education for your children which would leave you really short of cash (one holiday in cottage in UK a year, no real money for entertainment, fun etc). Told by parents there will be plenty of cash 'another day' but they don't like living with that in mind.
Option 2:
Throw caution to the wind and have another child that will leave enough money only for state education (average schools), but plenty of money for fun, house, investment etc.
Children concerned are bright. One is quite quiet and easily intimidated (not sure if this is relevant). This is something one of my best friends is pondering at the moment and not sure how to advise.