I would suggest the same as the folks before me. Find them good, honest "worldly" friends. That way they can see first hand that in most cases.....not only are "worldly" people not bad.....they are actually nicer than the "friends" they have at the kingdom hall.
Make sure they are NOT home schooled. As they see their friends at school celebrating their birthdays, getting into the Christmas spirit, having a blast playing sports etc etc........they will see that these things aren't bad at all.
My children are 5 1/2 and 3 1/2. My soon to be ex wife is constantly barraging them with how bad birthdays and Christmas and magic etc are. When the kids are with her.....they lead a regimented life.....dominated by meeting attendance and service. When they are with me.......I give them choices. Yes.....I believe that 5 and 3 year olds should be given choices. With me......I tell them "it is up to you". For instance.....my oldest wants to have a birthday party. 3 months ago she was completely indoctrinated. But kids have brains and curiosity. She asked me if I celebrate mine. I told her yes. She proceeded to tell me that Jehovah doesn't like that. I used basic reasoning with her. "Jehovah isn't happy I was born?" I asked. "I sure am happy YOU were born." She responded by saying "but birthdays put too much importance on one person (yes a 5 year old said this) and that is selfish". I said "but what about so and so's wedding you just went to. That day was all about them wasn't it?" She literally thought about it for a minute and said......."yeah.......so there's nothing wrong with birthdays?". I said "I don't think so". She promptly asked me if I would have a birthday party for her when she turns 6.
Even at such a young age......they are able to use basic reasoning. Combine that with her going to school now and she can see how normal kids are OUTSIDE of the kingdom hall. It is a desire for ALL kids to want to be normal. If you can catch them early......I think that TRUE love (not conditional love) and thinking skills will win out over forced indoctrination and fear.