Depends on your lifestyle I guess. Your tolerances for risk, fall-back money available to you, long term job prospects, health of the economy and housing market (sick as a dog), long term viability of your job industry, etc etc etc.
Also can't quite remember UK costs (and only left 3 years ago!
), but from memory I'd say anywhere north of 40k OUTSIDE London, and you'll have a comfortable life without counting pennies too much. Although, it's always a good idea to count them anyway. Or at least keep a close eye. But you can also live on far less.
Kids I have no idea as I don't have them. But I don't think they're as expensive as everyone makes them out to be. Again you'll be hearing that from people that don't really work optimally with their financial resources so it's hard to get an overall picture. What they THINK their kids need and what the kids actually need, would widely differ. My favourite 'parent' at the moment, and idiot of the month, wants to make his child's 'first Christmas special' and therefore 'saving hard' to give him a 'special Christmas day'. The kid was only born on the 24th last month.... So he'll be 11 months old come Christmas day. And no, I'm not making this up at all. When you have idiots like that out there, it distorts the realities of reality and you're left in fairy world watching how morons operate and complain accordingly. And let's be honest, us morons outrank you clever and morally honest people by many magnitudes
So, unless people can be morally honest and reflective for once, it'll be hard to know how much money kids really require.