Honestly, sometimes when I hear these people say it's hard to tell the difference either, but I know how it's supposed to be. First off the ending T's silent, not just barely heard like in English, but straight up silent. "-e" at the end in Norwegian is like a short "-a" at the end in English like in "Luna" or "sauna", but also at the front like in "above" or "across". Final "-a"s in Norwegian though are pronounced fully as "ah" like in "father" or "palm". So in English-y phonetic writing "barnet" is "bahrr-nuh" and "barna" is "bahrr-nah". At least that's how I've come to understand it so far.
Soda in British English means carbonated water. 'Lime & Soda', 'Brandy & Soda', 'Whisky & Soda' .. it's a mixer. It's not a drink with any sugar. Fizzy or soft drink is the term for any sweetened or unsweetened fizzy drink. Fresh drink implies fruit juice, like freshly squeezed orange juice etc.
Soda water usually contains either sodium or potasium compounds to give it a slightly salty taste. In Australia, we usually call the Americans' "soda" soft drink or lemonade (can be any flavour, not necessarily lemon, or plain), although due to the huge influence American culture has on Australian, most people would also understand "soda" with little difficulty.