As stated by someone else, your time with your children is YOURS. I would find out what the kids like to do for enjoyment and do various activities with them to crowd out "KH tine." You could let them take turns deciding what to do during their visit. The kids will remember how you made them FEEL, not so much what you said. If you want happy, well-adjusted children, you need to provide an atmosphere that fosters self-esteem and the ability to make appropriate choices, NOT the blind obedience of the WT.
You might want to talk to their teachers and other adults in their lives and explain the situation. You might also want to talk to a child development person about how to combat the blind obedience notion they are learning and the right strategies to teach them not to hurt or condemn others because they're not JW's.
Good luck!