On a serious note..
Get them art materials, good ones (not professional grade, but decent student grade where possible, not the fuck-awful barely pigmented pencils, pens that are dry before you open them, paper that won't take a mark or alternatively feathers out the ink the second pen touches paper. Nothing kills creativity faster than shit materials and then being told 'a bad workman blames his tools'. Children are already struggling with a lot of disadvantages due to their age/developmental stage, don't make crummy tools/materials another one)...
DO NOT caution them to be 'careful' with them or 'save them for best' etc - let them be free with it, encourage them to make marks, experiment with colour and shape.
Be enthusiastic about creating stuff in general, if they want to fashion the Taj Mahal out of noodles or build a life size flamingo out of discarded socks... (within reason...) go ahead.
This isn't a fool proof guide to producing genius artists - but feeling free to experiment and try things out boosts confidence. Evaluating your work and trying again at something builds skill and also resilience. Soldiering on through a 'messy' stage (every art piece has a messy stage, where it looks like an untrained monkey did it!) is a skill everyone will benefit from.
You might end up with fantastic artists, but these skills are transferable to all sorts of aspects of life, and learning.
I am an artist, but it has taken me a really long time to relax, let go and be free with materials and dare to mess up, waste stuff and make a mess. As a result, its only in my late 30s and early 40s that I really got somewhere, became professional and started actually earning money from it. I can also think of a lot of other areas in my life where the above applies!