Where to go Tonga/Samoa/Fiji?

I am traveling around the world with my wife and two small children. We have been offered a free stop on our way from NZ til LA. What would be greatest for a company with small children for a 2 weeks stop - Fiji, Samoa or Tonga. We are free to stop in any of the mentioned places. We will be going in April.

Thanks

I'd go for Samoa.

Fiji is probably the easiest with kids, but I found my experience - Nadi and the Yasawa islands - to be very touristy. Still, that counts in your favour if the kids need entertaining.

Tonga was great but the infrastructure isn't brilliant and could be tough with kids. Samoa is the happy medium for me.

1-Fiji

2-Samoa

3-Tonga

I haven't been to Samoa, but I'd pick Fiji before Tonga. As indicated above, tourist infrastructure isn't so good in Tonga, and the main island is no great shakes either. Lots more to do and places to go in Fiji.

Having just returned from a year of living/woking in S.Pacific (yes, with my family, son of 10, daughter of 12), and based on the situation you just described, I'd rank Fiji (Nadi) #1, Samoa then Tonga.
As I was based in Fiji, getting away from the tourists isn't difficult, yet Nadi and the various islands all of which are within a 30-45 boat ride gives you access to amazing beaches, snorkelling and yet solitude for the adults much better than the other island countries of Samoa, Vanuatu, Solomons, Tonga and particularly PNG (which I'd heartily recommend nobody with kids ventures anywhere near due to its pure violence factor).
All of the resorts around Denarau (a 'burb of Nadi) offer tremendous facilities for the kids and include brands such as Hilton ($$$$), Radisson($$$), Sofitel ($$ without compromising their 5 stars), Westin and Sheraton ($$$) although as we were leaving Fiji in August, the Sheraton was completely closed for a complete renovation.
Everything you may want from an experience can either be arranged at or available through the Denarau Marina which is the hub 'mall' for getting off the main island (Viti Levu) and out to the various resorts (Beachcomer, BlueLagoon, South Seas Islands, etc)...fabulous place with Fijians likely the friendliest people in S.Pacific along with Samoans, in our experiences.
Hope it helps.