Tips for parents:
My thoughts about supporting children's creative work
I'd provide the youngster with good materials and let them get on with it. You only need one or two paintbrushes, but they should each cost the equivalent of two or three cups of coffee in a Costa. Get some half-decent watercolour paper - a huge sheet, or a tear-out pad, should cost something similar to a decent paintbrush.
Their interest in writing or drawing may have come from books they've enjoyed with you, so obviously, keep supplying them with more.
What's wrong with praise?
It's natural for kind parents to gush and praise when a child shows them their work, but everything I've learned tells me to try and moderate this. The child did the work because they loved doing it, and that is the one most important thing you want to preserve. Shouldn't we all nurture the ability to do things because we love doing them? You don't want to get your child hooked on doing things because that will earn them your love (probably a big reason for writer's block among adults). You know you love them unconditionally, but they can misunderstand what's behing your praise or comments.
So how do you support your artistic child? I believe you should show a genuine interest in the only thing that really matters: their process. "Oh wow! Did you enjoy doing this? What do you love best about it?" If they're critical about what they did, listen and try not to get pushed into praise and reassurance. The world is full of people who don't like how I draw, or don't give a monkey's, and I can't base my life on other people's opinion. So you might say, "What is it about the horse that you don't like? I see." Listen carefully. You may think they hate their horse because it doesn't look anything like a horse, whereas your child may hate it because it looks sad. If your child wants to know if you like it (and usually they don't), it's OK to talk about your reaction ("I love those blues you've used for the sky, it reminds me of being relaxed on holiday"). Or maybe it will come easier to just say, "I love those colours, and that little dog makes me want to smile". The main thing is to avoid talking in terms of your child's attributes ("you're so clever/gifted"). Praise creates pressure for the future and takes focus away from the all-important process.
If you're intrigued by all this, I can recommend Alfie Kohn's book "Unconditional Parenting. Moving from Rewards and Punishments to Love and Reason".
Classes and how-to books
Offer to take your child to classes, but only if you sense they actually would like it. They may be exploring and learning perfectly well on their own. Check out the attitude of the teacher: there should be a focus on process and exploration, not on a cookie-cutter result.
The same applies to writing. On the whole, I find that kids are bursting with ideas, so you hardly need to give them any input there. Their stories go all over the place and may be full of inconsistencies, but they're doing extremely valuable and precious work simply by writing. Let them enjoy it, and if they ask for advice, be very careful to listen to exactly what they want, and stop as soon as you notice an urge to take over. It's their story, not yours. Not always easy.
"How to" books can be stimulating, though I'm not keen on pushing them at kids if they're quite happy with their explorations. There are many books on how to draw animals, cartoons, and so on. Only use them if your child actually wants to draw that way. Children under the age of 12 or so are quite happy drawing their own thing, and it's only later that they get frustrated that it doesn't look like a photograph.
So with all this in mind, here are some books I like.
Doodle Books have, thankfully, become quite common and are great alternatives to those creativity-draining, soul-sapping colouring-in books. Children are invited to draw things from their imagination. In the two examples here, The Doodle book has the most attractive cover, but I think The Anti-Colouring Book is the better one inside. I like the drawings in the books to be quite rough, so that the child feels free to draw their own way. The principles are similar to those in "Drawing for the artistically challenged", featured below.
Drawing for the artistically undiscovered by Quentin Blake and John Cassidy, is full of ideas to stimulate young and old and get you relaxed about drawing - you're supposed to draw straight onto the lovely paper, but I can't bring myself to do that.
How to be a brilliant writer by Jenny Alexander is a very safe bet for your child. Jenny Alexander is very much into creativity and playing with ideas, and doesn't believe in perfectionism or being seen as "brilliant", in spite of the title (publishers don't always get the titles we want!) This book isn't just for youngsters - I've enjoyed it for myself as well.