To go Voltaire here: I personally find it a bit sad when little kids are already scared of hell, as they most likely won't be at the crossroad for quite a while and there are better things to do in life than going around being afraid (of being inadequate, a sinner/sinning, etc). But on the other hand, I don't see how taking your children to church and Sunday school (assuming the Christian model here) cannot be seen a thing verified in reality. If you have a young child and do not wish to sacrifice your beliefs, you HAVE to bring it to church. And Sunday school is an excellent way to get a tiny bit of time off and getting some help with the raising of ones child. The services are also free (donations and Scientology excluded, I believe) and are social occasions. So they are not at all without benefit, even from a worldly perspective.
I concur with the sadness of deliberately placing fear in the heart of an innocent. However, if hell, fire and brimstone is the first lesson in Christian education, then I would suggest the syllabus needs an overhaul. Also, the teacher who teaches thus actually seems to have some fairly serious underlying issues of their own, and a sadly mis-prioritised understanding of their faith.
As to the original question, if you have a child whom you love, you want to provide the best for them. The best home, the best food, the best education, and the best advice. You would impart your beliefs to them because you have taken them on board yourself, believing, to the extent of your own knowledge, them to be the closest you could get to a universal truth. If you
didn't pass on your beliefs, it either means you are protecting your child from something which you know is inherently flawed, and therefore should discard for yourself, or else you are withholding something good to keep yourself, which may bring the depth of your parental love into question.
Personally, this is something I have actually put into practice. I have three young children, and I am doing my very best to pass on what I have learned. Because I love them.