Joanne Jacobs reports that the University of Sheffield in England surveyed kids and found out that they generally find clowns to be scary. Apparently they want to redecorate the children's ward at a hospital and someone (thankfully) thought it would be a good idea to ask kids their opinion.
I hated them as a kid, my siblings despised them and I don't think I had one friend who had good feelings about them. I find kids generally like their adults to be without masks and to behave, for the most part, like adults.
Stick to talking trains and cartoony woodland animals. 90% of kids will adore one or the other.