I'm an atheist and I tell my children adults invented Santa Claus so children will behave and go to bed early in the winter while the adults get drunk and fornicate with each other.
In fact, I instruct my children not to lie and to tell others the same thing if asked about it. I don't lie to my kids.
Now if you think that is bad, lie to your kids all you like and they will lie to you.
I don't want my kids to lie to me, and they expect the same from me...
My kids don't know what fornicate means, for now. If they unluckily meet your kids in the next few years, they'll probably just be shocked by their language and sorry for their lack of history knowledge. Kids like yours give me a good teaching opportunity for my kids and the society they are going to inherit. Someday, they'll probably pray for your kids, directly or indirectly.
Merry Christmas!