"Let children learn about different faiths, let them notice their incompatibility, and let them draw their own conclusions about the consequences of that incompatibility. As for whether they are ‘valid,’ let them make up their own minds when they are old enough to do so."— Richard Dawkins

One of the dangers of subscribing to this philosophy is your 3 year old marching around singing "This is the DAY, this is the DAY, that the LORD HAS MADE, that the LORD HAS MADE." She doesn't actually sing those words exactly, but that's the general idea.