Here's an expression I've recently adopted: "What you permit, you promote." Don't permit it. Take the team, sit them down, and have a conversation about disabilities. I'd suggest you find some examples of these types of discussions on YT. The discussion shouldn't be a scolding. It should be educating the little cretins, in an effort to help them grow into decent human beings. You're volunteering your time for these kids. They owe you a greater measure of respect. Respect is sometimes lacking in some households. But this isn't their home.