Liamsnana
These days children are being kept in nappies until they themselves express a desire to start using a potty or the toilet.
My foster-daughter told me it is DREADFULLY HARMFUL to start potty training before children are at least 2 as they do not produce the hormone that (apparently) controls the spincter of the bladder before then.
No point in arguing with a young mum who has read all the latest books and had the newest ideas dinned into her by health visitors and her contempories.
I have no idea whether this idea is a new, brilliant discovery or not, but it might well be the reason your three year old grandson is still in nappies.
My advice, which I am sure you have thought of yourself by now, is please do not even think about potty training until the little one has settled down with you and his new routine and changed circumstances.
Wait to the summer, and hope for warm weather, so he can run around in the garden med no nappy or trousers on. Then produce the potty.
Little boys often respond well to seeing granddad or some other male relation weeing into the toilet. Is there a male relation around to casually forget to close the toilet door?