I wouldn't go with impeding, as I don't see anyone in the scenario preventing another from playing the ball. My solution is as follows:

No pass back to the keeper because the angle is wrong. The keeper came out and got it. Might it be a set play? A clever coach might attempt it, but the risk of a pass across the face of their goal probably isn't worth it.

The whistle is incorrect. Since no infraction occurred, the restart is a drop ball. Since the keeper had possession, I would drop it to the keeper. I would also violate the literal reading of the LotG by declaring that I am dropping to the keeper. These are kids after all, not pros.

and to throw in... impeding could potentially be an option? Thoughts?

and besides red cant be offside if his team isnt playing the ball... since blue was playing the ball deliberately, I would have gone with the back pass since the kicker deliberately ran out and grabbed the ball and IFK to red

Exactly, originally I had included "As you're walking towards the point of the infraction you're questioning if you made the right call."

So now, assuming that the ref realizes it was a poor call, what to do?

Personally I would probably do a restart with the keeper and explain to both coaches that given my angle and view I made an error, unless I believed that R3 was interfering with B1 (GK) playing the ball.

After the game I'd probably mention to Red coach that a back-pass (if deliberate) would have resulted in indirect kick and not a PK.

I waited long enough. My question is: Why did you blow the whistle?

Dan, you're going to love Expo sooo much... ;)

I have one question, but I'm going to wait for others to join the fun.