I think this is actually a very good idea. I'm a HUGE weather/geology/geography junkie - have been since I was very little. One thing about tornadoes people don't realize is that the majority of fatalities that occur during a tornado are from people getting impaled by the debris; so, by making these things bulletproof it really serves a similar purpose in protecting children from wooden splinters, nails, shattered glass that is traveling over 100 mph. Doubling as an earthquake shelter is also very smart, especially in Oklahoma as they've had a increase in earthquake activity over the years due to fracking operations (this is something that's denied by the government but is painfully obvious when you study the data).
Another thing about tornadoes, eventhough storm prediction and warnings have come a long way, I don't think people realize how fast a storm can literally go from non-existent to a super cell producing a major tornado in the span of just a few minutes. Even with the absolute best warnings imaginable, there is no way to prepare for those worst-case scenarios where these shelters would be the most useful.