Being in a 4wd shop will probably make you all think that I would choose the Prado. Only because that's the one I've had the most exposure to. Territory's are a nice vehicle, haven't had any come into our shop with dramas (only getting towbars fitted, etc), but I think their interior lets them down (not keen on the very plasticky, easy to mark finish). I don't know anything about the new diesel ones (I haven't read up on them), but even though they are diesel, they still may be underpowered (meaning you pedal it harder to go anywhere thus burning more fuel, or you will just be all-round dissatisfied with its performance - or rather lack of). Just a point to consider with any diesel vs. petrol vehicle choice.

Kluger's, I haven't had much to do with, so can't say much. Aside from a 'nice softroader'.

So, I might choose a Prado. Also the biggest of the lot. (And you can get more things for them like bullbars, lift kits, and off road tyres for them. Ever seen muddies on a Territory or Kluger? lol If that's what you want though!)

And yes, you can get extra child seat points fitted to vehicles. Some are more difficult than others, but often possible.

Lastly, have you looked into the safety ratings of these vehicles? Passing single lane at 100km/h, you may want to consider this. If you're looking for rollover protection, from what I last heard, the Porsche Cayenne is the only 4wd with it (don't we all wish we could have one of those!) This factor may help in your decision. Good luck!