Perhaps you can try seasoning with things that naturally contain salt, instead of adding salt, like cheese. And also the texture, a lot of kids like the crispiness of the breading of fish fingers.
Despite having had mixed success with crumbong fresh fish and meat before starting this thread I think the real winner has been mixing grated cheese with the crumb. He really does seem to be going for it.
He ate real fish crumbed again a couple of days back and yesterday ate more chicken than I've ever seen him eat before, 4 'nuggets' of about 2-3cm square which is LOADS. So I wanted to say thanks to everyone who offered their help and a particular thanks for this suggestion of cheese.
I did chicken thigh cut into pieces, dipped in flour, then tom puree watered down, then breadcrumbs with cheese and mixed herbs. Then fried.
He loved them.
It still isn't 'real' iyswim, but i think over time I might reduce the crumb to one side of the meat/fish and perhaps wena him off the breadcrumbs. For now breadcrumbs with cheese are a winner and at least I know he is gettng a mix of protein sources and flavours