Its early in the season.
Snakes are coming out of hibernation.
They are hungry, and they are looking to mate.
They also don't 'hear' the way you do (although they do
hear), vibrations from the ground are their main source of information about what's going on. Obviously, a
snake isn't likely to register the sound of playing children as something to avoid - the vibrations are more likely to do so.
If you're between them and the place they're going, they will appear to chase you. Move away at an angle, don't go in the direction they're already headed.
Snakes will respond if you attack them or they feel threatened - so don't approach them, don't chuck things at them, and basically leave them alone. Give them a wide berth, and they will go about their business and ignore you.
And if you're really concerned about snakes in your yard, check out the vibrating
snake repellents. The snakes in our local area move through areas with the repellers installed very quickly, if they have to go through there at all. Much better than having a
snake set up residence.
Finally, I hope you're all up to date with your first aid skills and know what to do in the event that a person or animal is bitten by a
snake.