Why did the TARDIS take them to the Doctor's childhood and why didn't she want the Doctor to know where they were?

Question

In season 8 episode 4, Listen, after they were at the end of the universe and the Doctor is knocked out, Clara uses the TARDIS telepathic circuits to escape. They end up in a barn. Clara checks out the situation and hides under a bed from the parents of a child who is present in the barn. Then she realizes the child is the Doctor and tells him something to always remember:

CLARA: Listen. This is just a dream. But very clever people can hear dreams. So, please, just listen. I know you're afraid, but being afraid is all right. Because didn't anybody ever tell you? Fear is a superpower. Fear can make you faster and cleverer and stronger. And one day, you're going to come back to this barn. And on that day you're going to be very afraid indeed. But that's okay. Because if you're very wise and very strong, fear doesn't have to make you cruel or cowardly.

CLARA [OC]: Fear can make you kind.

CLARA: It doesn't matter if there's nothing under the bed or in the dark, so long as you know it's okay to be afraid of it.

CLARA [OC]: I'll show you. So, listen. If you listen to nothing else, listen to this.

CLARA: You're always going to be afraid, even if you learn to hide it. Fear is like a companion. A constant companion, always there. But that's okay, because fear can bring us together. Fear can bring you home. I'm going to leave you something, just so you'll always remember, fear makes companions of us all.

Then she went back to the TARDIS and said:

ORSON: What happened? What did you see? What's out there?

CLARA: What if there was nothing? What if there never was anything? Nothing under the bed, nothing at the door. What if the big bad Time Lord doesn't want to admit he's just afraid of the dark.

DOCTOR: Where are we? Have we moved? Where have we landed?

CLARA: Don't look where we are. Take off, and promise me you will never look where we've been.

DOCTOR: Why?

CLARA: Just take off. Don't ask questions.

DOCTOR: I don't take orders, Clara.

CLARA: Do as you're told.

Why did the TARDIS take them to the Doctor as a child and why didn't she want the Doctor to know were they were? What did he see when he was knocked out? Why did she say that speech to him as a child? I thought the speech was to know his future was in safe hands as his future regenerations Hartnell-Capaldi.

Answer 1

The answer lies in the very same episode you just quoted. The TARDIS telepathic interface works in such way that it explores the "plugged" person's entire timeline in order to find the wanted destination, like it was explained earlier:

(The Doctor places Clara's fingers into squidgy sections on the Tardis console.)

DOCTOR: Just hold on tight. If anything bites, let it.

CLARA: What is it?

DOCTOR: Tardis telepathic interface. You are now in mental contact with the Tardis, so don't think anything rude.

CLARA: Why not?

DOCTOR: It might end up on all of the screens. The Tardis is extrapolating your entire timeline, from the moment of your birth, to the moment of your death.

CLARA: Which I do not need a preview of.

DOCTOR: I'm turning off the safeguards and navigation, slaving the Tardis to you. Focus on the dream. Focus on the details. Picture them, feel them. The Tardis will track on your subconscious and extract the relevant information. It should be able to home in on the moment in your timeline when you first had that dream. And then, we'll see.

CLARA: What will we see?

DOCTOR: What's under your bed.

(He starts the Tardis flying.)

CLARA: Ooo!

DOCTOR: Okay, now don't get distracted. Remember, you are flying a time machine.

(Clara's mobile phone rings, and the image of Danny greeting her at the restaurant flashes into her mind. As the Doctor walks around the console to her, he passes a blackboard with lots of items chalked on it, beginning with Evolution Perfects. It is what he wrote at the top of the show.)

DOCTOR: No, no. Don't you dare. No, don't. Don't, don't. Just ignore it.

Since Danny called Clara to her cell phone, she started thinking about Danny and that's why they ended up in HIS timeline, when he had that same nightmare, instead of hers.

Then, right at the end when the TARDIS ended up in the barn in Gallifrey with the child Doctor, the answer seems simple: Clara was thinking about the Doctor when she set the TARDIS flying, and once again, it (she) took them to the night the Doctor had that same dream.

As for why Clara didn't want the Doctor to know where they ended up:

As the Doctor himself had told Clara earlier in the same episode:

CLARA: Isn't it bad if I meet myself?

DOCTOR: It is potentially catastrophic.

CLARA: So why did you bring me out here?

DOCTOR: I was still talking. I needed someone to nod. Probably best for you to wait in the Tardis.

So yeah, it's potentially catastrophic if the Doctor finds his younger self, apparently (Except for those times when he has done exactly that, in the multi-Doctor episodes).