K and G are the consonants in most western languages that are hardest to learn how to say. What ways can I help my kid(s) to learn how to pronounce these sounds?
The way we taught our three was the same as with other sounds - sitting with them and showing them how the mouth and tongue move when making these sounds.
Best bet is repetition of sounds like ke ke ke ke ki ki ki and words like kicking, get, give etc as they got older.
They actually got K and G really quickly. We actually had much more difficulty getting them to distinguish between Th and F, even though the tongue position is obvious.
Depends on the age. It's most easily done when they are young (1-4 years old) and their phonem maps are still forming. In this case they just need to hear it (frequently and correctly) and need to regularly interact with native speakers. When we moved to an English speaking country, my kids often listen to a tape of "Thomas the tank engine". They happily listened to it without initially understanding a single word. In conjunction with play-mates and pre-school they quickly spoke fluently and accent free including the sounds that are tricky for Germans (e.g. "th" or "v" vs. "w" sounds). More formal training is probably only useful for older kids.
Very important to make sure they have normal hearing. If there is any doubt, get a hearing test to test all the frequencies of speech.
Then make sure they have lots of examples to listen to. You can make them tapes of words that have the sounds at the beginning, middle, and end, as well as words that have the sounds before and after different vowel sounds. Check out http://www.soundsofenglish.org/pronunciation/gk.html to learn more.
Songs are another way to help them learn. Choose some songs they already know and point out the sounds. If you don't know any, try: http://www.songsforteaching.com/earlychildhoodelementarypreschoolkindergarten/funnyrhymes.php