Plenty of reasons why you might say that. Most dogs can't digest chocolate, for example. Also, as a guest I sometimes bring a gift of liqueur chocolates, obviously for adults only, so I would probably say "Those sweets are not for you, but for your mother - these sweets are for you."
No. "I went to get some lolly" means "I went to get some money". It does in British English anyway. If you are after lollipops you would say: "I went to get some lollies". If you are after any kind of sweets you would say: "I went to get some sweets." I'm still uncertain whether "slik" means "sweets" or specifically "lollies" (as in the picture). Can someone explain please? Not that I want any. They are all bad for the teeth.