My Grandparents had a spaniel when I was very little, and Gran decided she needed a course of Bob Martins tablets (the spaniel that is).

Judy, the dog, used to live on a diet of dog biscuits and leftovers. Anything put on her white tin plate, she'd wolf it down. Grandad brought a whole rabbit home one night, and Judy scoffed the bits such as...you don't want the details.

They decided to buy some tins of dog food and mix two Bob Martins with each meal. Judy always bolted her food so fast, they hoped she'd not notice or care about the tablets and down the hatch they'd go.

I sat at the kitchen table and watched Judy get her plate of glistening chunks and rich brown gravy, spiked with the tablets.

I sat and watched, my little feet dangling high above the kitchen lino.

Gobble gobble gulp.

All gone in 45 seconds, followed by the licking of the plate. Judy always licked clean. But hang on...

Something different this time. I hopped down from the kitchen chair and crept to peer over her shoulder. The plate was cleaning up as usual. Except for two perfectly round, bright, white Bob Martins which had been expertly pushed onto to the blue rim of the plate, and sat there, side by side as the final licks were going this way and that.

Then she walked away.

I thought I'd never again in my lifetime see such sophisticated, instinctive, determined avoidance of something that is good for you.

And then I fostered.

Vegetables, fruit, vitamin tablets, brown bread. Tap water.

You apologise that the only crisps in the cupboard are plain ones, you get a look as if to say "I told you already, none of your health food."

Not just food and drink: bedtime, reading, wearing a coat, brushing teeth, walking (anywhere).

We've had a taste of this problem with our own children, all of us. But it is magnified in looked-after children.

If it does you good, they spot it a mile off. No chance. However if it rots your teeth, guts, and mind, if it turns your brain to jelly, if it hardens your heart... Gimme!

I was at a lecture about self-harming a few years ago and when we had a ten minute break half the room went outside for a coffee and a cigarette.

I asked the lecturer if they were self-harming. He said no, because the fulfillment lay not in the harm or danger. I'm still unconvinced. I've got it in my head that looked-after children, who often crave "control" more than anything else, reserve the right to do the wrong thing with their body and mind, because, let's face it, the poor loves; it's the only thing they've got left for sure that belongs to them.

So at Blue Sky, the training tells us that if they come downstairs dripping blood from a sliced forearm, we say "Are you okay? Do you want some paper towels?" In other words, don't make a big deal, or try to argue the toss, just offer love and help.

So maybe, when they want a dinner of prawn cocktail crisps washed down with a blue Slush Puppy, then be the last to go to bed, we sometimes go with the flow.

Gran finally got Judy to swallow her Bob Martins. Every night for a month Grandad would hold her jaws open (the dog's) and she lobbed them at the back of Judy's throat.

And there are times when we have to dig in too and stick to our guns.