I'm so GLAD you brought up this subject... I am very aware of this and how "worms" can be transmitted to children just in the playground or our own yards.
For THIS reason, I have always told my kids to ALWAYS wear shoes outside (here where I live many people go barefoot and at the beaches). Worms, hook worms, tape worms, pin worms, and round worms can be picked up via bare feet outside, and the parks have stray animals or even pets that go and do their pooping at the parks and playgrounds too. So gross. My friend got tape worms this way, for example.
Just wanted to thank you for this subject. It's very important, and yucky!
Perhaps, search online for ways to rid the yard of the roundworm and eggs.... I"m sure there are things that will come up in a Google search.
All the best,
Susan