Sorry, but that term is already off the great euphemism treadmill of political correctness. The proper way to refer to someone suffering from mental retardation would be to refer to them as one with “special needs” or an “intellectual disability”.
Seriously though props to you for helping out with kids like that. While I’m no saint and will admit I got a few laughs out of that thread, I just can’t imagine what it would be like to go through life like that.