Why do security guards search older women and little kids at airports?

I cant believe how security guards are too over protective at airports and they search the most innocent people! Like for an example, handicapped people in wheelchairs, older people, and little kids! I mean, really thats absurd! Do the security guards really think little kids and older people are terrorists and have a bomb on them?!! That's a waste of time! Why not just let a little baby get by in the metal detector or a person in the wheelchair without being searched?! They are harmless!