Sorry I Only ever do quick posts due to my 2.8 & 5yr old around so I'll be brief
What do you mean by decent beaches? Having come from the UK where we would have had to spend a couple of hours driving to the nearest & very crowded beach I find the ones in Wellington to be great, you have Oriental Bay in the city then driving out Scorching Bay is nice & lots dotted along the way the other end or us we have Titahi Bay which can be nice then further afield up the Kapiti coast Paraparaumu Beach & Raumati Beach which is about 45 min drive but has long stretches of beach, head this way for Queen Elizabeth park & more bush walks, I know a friend went camping for the weekend in Paekakariki. Oh & there's Pukerua Bay on the way for another beach
We are not into the walking part yet so can't comment on that so much but for children in Wellington there are so many things to do & think it's a great place to bring children up.
Good idea may be to go onto Google maps & scroll around the Wellington area to see how close things are, I haven't mentioned anywhere in the Hutt valley or Wairapa where I'm sure there's even more but not had the chance to see yet, it looks lovely there too, there is loads around & I can't wait to explore more there's just too much to see & not enough weekends in the year to see it all.
Hope this help a little, please feel free to PM me if you need anything more
Lindsey
NZ Expo London 13/10/07
OH Job interview/offer 17/10/07
EOI submitted 21/10/07
EOI selected 24/10/07
ITA handed in 03/12/07
Arrive Wellington 11/01/08