Amazon have an amazing offer on Outdoor Crayons, perfectly timed for summer fun. For £1.20 you can buy a set of 15 sidewalk crayons in bright, bold colours. It's reduced from £6 on Amazon, and everywhere else I could find it was over £10. It's a great price, and will make for fun birthday present add-ons for the coming birthday season. Even with the hefty shipping fee, it's a lot cheaper than elsewhere.
My children love their outdoor chalk board. While they have three chalk boards in the house, the one that sees the most use is the one in the garden, where the rain washes it clean and they get to stand up and draw on a them-sized board. They also love drawing on the fence and the paving, and with these great big outdoor chalks, that's not a problem at all.
These crayons are oversized chalk and not as brittle as your run of the mill chalk. They have bright and bold colours, apparently particularly the yellow and pink which look neon in the bright sunlight. One of the reviewers says that though they do also break sometimes, they break cleanly meaning youngsters can still use both parts, which is great.
The chalk cleans up really easily, with just a splash of water, or rain making a perfect no effort canvas, and a no chalk dust to have to clean up either. Bonus.