The /k/ sound can be a tricky one for some kids to learn because it’s hard to see what speakers are doing with their tongue at the back of the mouth.
If the child is fronting
Keep the front of the tongue down by opening the mouth wide or using a tongue depressor to hold down the tip of the tongue while the child opens their mouth and makes the /k/ sound.
Tell them to lift the back of their tongue up to the roof of their mouth to make the sound, while keeping the front tip down by their lower teeth.
Shape the /k/ sound from a cough
Have the child do a few pretend 'coughs' and see if they can make the /k/ sound 'in the same place' as the cough.
If the child is backing
Use high front vowels as a facilitating context to help them keep the placement forward.
For example, words like 'key' and 'kite' encourage more anterior tongue placement, while target like 'coo' and 'cook' are likely to be more challenging.
Minimal pairs activities
Some children also get confused between /t/ and /k/ productions, and can benefit from working on minimal pairs activities, where the task contrasts words that differ only by whether they have a /t/ or /k/.
Conclusion
Having children work on these contrasts can help to achieve that 'aha' moment which lets them understand why they’re working on these sounds in speech therapy!