In addition, it seems like there's some kind of bonus/reward for kids savings (1% on $4.99 plan, 5% on $14.99 plan). I'm not sure how this works, but this might make things even more lucrative.
ETA: looks like this is a rate on up to $5,000 in savings per family. Works out to an extra $200/yr for spending an extra $120 on the subscription.