I decided to do an experiment. My six-year-old brother decided to try FE3H, but couldn't do too well, so I decided to see how well he'd do in FE7. I put him on Lyn's normal tale for the sake of actually giving him a tutorial, and he actually did fairly well. Up until about chapter three.
He got Florina killed hilariously quickly, she was dead by the end of turn 3. He also managed to lose Dorcas on the last turn of HIS join map. Then, he basically threw Matthew away on Chapter 7 by trying to make him fight a shaman. He then asked if he should send Rath in against said shaman. It sounded good to me, so I gave him the green light. He forgot to tell me that Rath was on 13HP and wouldn't survive EP...
He's still got both of the cavaliers, though, so he should be fine. I plan to at least get him through Lyn's Tale.