Fed up with cat. How to stop her from getting up at the crack of dawn???

[Belgianchocolates]

Now my DC's are finally old enough to sleep through the night it's our cat that's waking me up .
I never ever feed her before 7.30, because that's the earliest I want her to get up. I also lock her into the lounge, because otherwise she goes and wake up my ds (her favourite person in the world) at 5.30 am, who then does feed her.
But now, about 2x a week or so she wakes at 5.30 (usually mornings where I am not working and can have a longer sleep) and then bangs into the lounge door relentlessly. I think she's trying to knock it of its hinges or break a hole into it, which is not going to happen as it's a sturdy door and only a tiny (adult) female cat .
In the end the noise always wakes me as I sleep right above the lounge. It's the only room we can actually lock her into as the kitchen doesn't have a door and the dining (also known as junk room) has a cat flap as her litterbox is kept in there (we never actually eat in there).
Tell me, what are we doing wrong and how can we encourage her to sleep a bit longer or at least stop her from trying to break through the door.

We live in the middle of nowhere and I've never once had mice/rats/foxes coming in through the catflap .
Yes cats may bring in mice/voles/worms/moles etc but they are cats. It's what they do.
I'm sure the cat wouldn't find it too cold. Ours have used the catflap from about 3 months old and come and go as and when they want. They spend hours outside in the cold/rain/snow. They have fur coats.
Leave some dry food out before you go to bed and let her get on with being a cat .

With the term breakfast I was refering to the time of day that I feed the cat i.e. morning. We don't actually give her a proper cooked breakfast of eggs and bacon if that's what u had in mind, just some Felix will do

Get one of these and put it outside your back door with a nice cosy blanket in. Really, cats don't freeze to death if they stay out all night!

I know my cat and she WILL jump on the windowsill and wake us up if she can't get into the main house in the middle of the night, just as I know that she WILL wake my ds(6) first thing in the morning (i.e. 5.30) if she is allowed to roam the house as he is her favourite person and when I let her out in the morning she always shoots up the stairs and into his bedroom before even having some food or visiting the litter box! He's too little to be able to ingnore her and turn over, so I've got to do something to let him have his sleep and unfortunately it's leaving the cat in the lounge overnight.
A lot of the comments on here make me feel cruel, but what would you do if your cat woke your son? Keeping her in the lounge overnight seems to be the only option so far, but obviously is causing trouble too.

I know exactly where you are coming from on this. We have an oriental cat that we have to lock in the kitchen at night - partly because we dont want him going out at night as we live on a busy road and dont want to risk him being run over like my last cat ... and partly because if we dont keep him locked in he spends half the night jumping all over us in the bedroom and I am a really light sleeper (my previous cat used to come to bed when we did and sleep through until morning .. it was fantastic). That said he has now learnt how to open the kitchen door if we ignore his cries for a long time. The second he hears ds make a noise or one of us go to the bathroom he starts up in the morning. We had such problems with his crying when we first got him we had to go and get him a friend ... so now we have 2 mad cats locked in the kitchen every night. It has certainly helped the problem as he has company and it has stopped the crying during the night .. it is just first thing in the morning now! Perhaps a friend for your cat or the radio on low might be worth a try?

Get another cat to keep her company .
How long have you had your cat? How old is she? Have you had pets before?

Why can't you let her come and go as she wants and just shut your ds's door?

She's a cat. She has a fur coat. She will not freeze to death overnight in the utility room.

I'm not worried about her freezing to death, or anything, but if we don't open the door between the kitchen door and the utility she'll just go looking for a window sill and miauw until someone lets her in properly. She's woken the ap in this way plenty of times when we're out in the morning. I'm pretty sure she'll do that at night.
We've got funny doors they push open, so can't be closed properly. All the cat has to do with my ds's door is bang into it often enough and she's in. If it was that simple, we'd have sorted this ages ago.
The cat adopted our family about 9 months ago, she turned up and loved it here. I put notices up in the hope her owner would claim her back, but no replies. The vet estimated her at about 9 months when she first turned up, so she's about 18 months now.
I grew up with dogs, chickens, geese, guinea pigs, hamsters, gerbil and my dad even had honey bees. But unfortunately I only ever had cats until I was 6. All I remember is that they lived in the conservatory at night and so there was no problem.

I don't see why a cat can't live in a conservatory (or other shut room) overnight -it's not as though it's going to be for weeks on end. Some cats never leave the house they live in.