Last year my children gave me a Bonsai tree for Mother's Day. I have
absolutely no experience or knowledge about them at all. Is there
anyone out there who could offer me some advice on how to keep it
alive?

It is called 'Tree of a thousand stars' according to the book I've
bought. So far, more by luck than judgement it has survived but it is
now starting to look a bit sick and the leaves are turning yellow and
dropping off!!

Any help would be welcomed.