Previous threads with good info and opinions:
TAB Users
TAB Bikes
If you can make up the difference between your father's contribution and the cost of a Burley, I would do that. Otherwise, the Adams and Trek seem to be the better of the seat post hitch tabs. I have not heard much about the Novara's but I would guess they are about the same as the Trek and Adams.
One of the best deals going is the used market. There are a few Piccolos on Craigslist. They generally go for under $200. If over then I would definitely offer less. There is one near me in DC, but it is listed at $200. Of course there is shipping on top of the cost, but you could get a Piccolo for the cost of a new Novara.
If the ride is not that important and you just want one that will work and no hassle shopping, the Novara will be fine.
I'd recommend gears over single speed. They generally don't start to use them until ~6, but it is nice to have when you do more varied terrain with wider speed ranges. It also helps them get used to gears for their individual bikes.
Good luck, post back with what you get.