Thats up to them isn't it?
From what i saw of their documentary all the children were very well behaved, lovely manners, had respect for each other.
And from my own experinces having a lot of children isn't a nightmare (dunno about teenage years tho!) Mine are all intelligent, starting their GCSE's a year early, are very patient, have huge circle of friends.
Some parents find having more than 2 or 3 children no big deal. Some can cope, some probably wouldn't.