The X Factor judge has been a patron of UK charity Together for Short Lives since 2009, and said that the organisations are "about joy".
"Whatever charity you support, you've got to see what you're supporting," he said. "I meet the kids, the helpers and the families and it changes your life."
Cowell was talking to Gethin Jones on ITV1's Daybreak to celebrate Children's Hospice Week, which aims to raise awareness and support for children's hospices between May 21 and 25.
When asked what happens when he visits the children, Cowell said: "They throw things at me! I have fun with them. You treat them like normal kids, because they are, they're just ill. It's about joy, and seeing that [hospices] are not awful places to go."
He added: "The government have increased the funding, but its private money that keeps these things running. Whatever your vision of what a hospice is, go down to see these places - it's not what you think."