Copied from the “scary for kids” website:
According to the legend, Hello Kitty was created back in the 1970s by a Chinese woman. Apparently, her 14-year old daughter was disagnosed with cancer of the mouth. The doctors told the mother that her child was terminally ill and there was nothing they could do for her.
When her daughter recovered from her cancer, the mother kept her promise to the devil. She created Hello Kitty.
The designers created Hello Kitty without a mouth because they wanted make her emotions ambiguous. The blank expression means that you can project your own emotions onto the cartoon. If you are sad, then Hello Kitty looks sad. If you are happy, then Hello Kitty looks happy. Hello Kitty will seem to feel whatever emotion you are feeling.
So, the truth is that Hello Kitty is not associated with satanic rituals or devil worship at all.