The meaning of 'That's tellin's,'

Question

'Sorry! It's all right,' said Una, rubbing her nose. 'How many rabbits did you get today?'

'That's tellin's,' the old man grinned as he re-hoisted his faggot. 'I reckon Mus' Ridley he've got rheumatism along o' lyin' in the dik to see I didn't snap up any. Think o' that now!'

They laughed a good deal while he told them the tale.

This is from "The Tree of Justice" in "Rewars and Fairies" by Kipling.
http://www.telelib.com/authors/K/KiplingRudyard/prose/RewardsFaries/treejustice.html

I do not understand the meaning below.
'That's tellin's' "
Is this mean 'I have got many rabbits'?

I ma glad if somebody kindly teach me.

Answer 1

You slightly mis-transcribed your quotation.

That's tellin' is dialect for That's telling, with telling used in the sense of disclosing that which is moral or prudent to keep secret. When one sibling tells on an other sibling to their parents, that is a great sin of childhood. The old man is refusing to speak while giving a motive that will seem reasonable to children.