Yes, under 17, and I presume so for the original post.Following those steps on TurboTax Online give the same result - just as mentioned earlier in this post.
As for me (married, jointly filing, 2 kids, AGI < $100k), first round was $1200 + 1200 + 500 = $2900 instead of $3400. Second round was $600 x 3 = $1800 instead...
I'm having the same problem: married filing jointly with 2 kids (4 and 1), but didn't receive stimulus for one kid on each check. I've not found any resolution ...