There are so many variables
Are you hoping to go straight from rental to a house, or work your way up the property ladder a couple of times?
Do you have family who would help out with childcare or are you going to need full time childcare?
Do you mean Wimbledon Proper or would you consider Raynes Park, Morden, Motspur Park? You will get lot more for your money in SW20 than SW19
Rough monthly costs:
Mortgage of £450k (Assuming you buy a £550k family home with a deposit from selling a flat) - £2k
Mortgage of £300k (Assuming you buy a 335k flat as first time buyers) - £1300
Bills - £500
Food and essentials shopping - £500
Full time childcare for 1 child - £1500
Travelcard £200 a month per person
So the bare min is going to be around £4K month household income if you have a flat and one child
If you want a house and 2 children, it's going to be a more, especially if you have 2 in nursery at the same time
That doesn't leave much/anything for savings, holidays etc
Less if you don't need a travel card to commute, more if you need a car
£5k a month is probably more realistic and that's roughly 2 people on £40k a year or one person on £90k
A household income of £80-90k will get you a mortgage of £350-400k so as long as you can get the 10% deposit
But like I said, there are lots of variables