Gee, that f2p model sounds familiar...
Though i think for a game aimed at kids, i would want to keep the moneysink dangers low, so a sub models sounds to me more appropiate (though a clever model where parents buy a certain limited amount of points per month might work too).
This said, i doubt that per definition it can be a big success (why should i sub as a kid for a game with many limits, when i can have the real deal a LOT cheaper? It looks like a fun niche game again, so far best for players with the money and nostalgia).