Could this be the correct call

Not enough information. Why was the batter sent back to second? Had time been called before he reached third? Had the ball been momentarily out of play?

If the runner legimately ended up a second base, he can't be credited with a triple. If the umpire erred in sending him back, I think you still have to only give him a double unless the game was successfully protested.

Doesn't the batter (now runner)location depend on where he was when R1 missed 3B? If the batter had made contact with 2B BEFORE R1 missed 3B then it would be a double. If the batter did not make contact with 2nd base by the time R1 missed 3nd base then the runner would be sent back to 1st base and given credit for a single.

The trouble here is knowing where the batter was during the point R1 missed 3b. Most of the time both runners aren't seen so an assumption is made by the umpire that the secondary runer had successfully advanced before the missed base incident.

There was actually this situation in MLB last year but with runners on 1B (R2)and 2B (R1). R1 missed 3B and appeared to score, R2 came around and also appeared to score. The batter was now standing on 2B. The play was appealed saying R1 missed 3B. Appeal was granted. R1 was out, R2 was sent back to 2B because he of course never made contact with 3B before R1 missed it)and the batter was sent to first.

I'll never forget this because instead of having two runs, the batter having credit for a double and 2 rbi, everything basically went back to the way it was (runners on 1B and 2B) but now with one more out than before the play started.

jfsbndr
I don't believe that a miss by a preceeding runner affects the status of following runners, unless there are two outs.

There happens to be a caseplay in NFHS which closely matches the scenario you mention. From the casebook:
"8.2.1 SITUATION B: With R1 on second base, R2 on first base and no outs, B3 doubles. Both runners cross home plate, but R1 fails to touch third and (a) R1 gets back to third before ball arrives at third or (b) after all play has ended, the defensive properly appeals the missed base by R1 and the umpire calls him out for failing to touch third base. Does run by R2 count? RULING: In both (a) and (b), the run by R2 counts. In (a), if there is no defensive appeal, the play will stand. If the defense properly appeals, R1 will be called out as he cannot return to correct a missed base when a following runner has scored behind him."

I think scenario (b) shows that there must have been some other aspect of the play you mention which caused the runners to go back. I believe that all rule codes treat this situation in the same way.

The batter was on third and the runner had scored. The other teams coach appeals that the runner did not touch third after the play was over. Then the umpire called the runner that missed third out and then sent back the hitter to second.

Son says it should have been scored like this - runner is out and batter stays on third or a tripple instead of getting sent back to second and scored a double.

The batter was rounding second as the runner that missed 3rd base was rounding 3rd base.