I'm pretty sure they know what their seven year old can and cannot handle and remember, and I'm sure they're familiar enough with the show to know its themes, etc. It's recommended 12+, but I have seen younger kids in the theatre who were engaged. All children are different, and I'm sure the OP knows their own well enough to make a judgment call.
In answer to the question, no, the seven year old probably wouldn't be able to see from SRO. You can request a cushion (or even two) to stand on (which might be helpful for the 12 year old), but I don't think it will make much difference for the younger one. If you want to take your kids, try front mezz. It's probably the best view for someone extremely short just based on the angle and elevation. Otherwise, orchestra seats on the aisle might be okay, since they'd be able to look out that way instead of over heads.
Updated On: 9/9/18 at 11:15 PM