Random Acts of Kindness Day takes place in the USA on February 17. In New Zealand, it's September 1. It probably doesn't matter when we celebrate it, so long as we DO! Being kind to a friend or stranger, for no reason at all, seems to me a way to give society a little nudge in the right direction.
Wherever there is a human being, there is an opportunity for a kindness. ~ Seneca
The Random Acts of Kindness Foundation has a website dedicated to "inspiring people to practice kindness and pass it on to others." It has resources well worth reading and discussing with your kids, including kindness ideas and inspirational quotes. Here's a quote that resonated with me:
Gratitude unlocks the fullness of life. It turns what we have into enough, and more. It can turn a meal into a feast, a house into a home, a stranger into a friend. ~Melody Beattie, Author
If you and your child are looking for just the right act of kindness to practise, browse through the list at the website. Teachers will love the graded lists of lesson suggestions too eg this one for preschool. Here's a video (Thanks@larryferlazzo!) that might give you some inspiration - "Watch as the camera tracks an act of kindness as it's passed from one individual to the next and manages to boomerang back to the person who set it into motion."
Sadly, I think we also need to discuss safety concerns with our kids when we talk about being kind. I wish we lived in a world where we could always be spontaneously helpful and kind. But we don't. You might decide to be kind to others as a family, or discuss times where you know your child will be safe and able to reach out to others. The important thing I believe, is to concentrate on being kind where we can.