Title says it all. All they need is suspicion. This can come from even an anonymous call to their toll free phone line.
A friend of mine had Six police officers come with a CPS agent(who incidentally was an obvious Homosexual) into their home and remove his five year old son who had a scrape on his knee from falling off his bike. Apparently his sons teacher saw the scrape and was concerned the boy was being abused. They have absolutely no proof and don't need any. The federal govt pays the state generously for every child in custody. Three months later he is still in custody(even after a chain of court dates accomplishing or doing nothing)
The only two states that do require proof of abuse before the removal of children are New York and California.
There was an incident where someone repeatedly reported the Oklahoma director of CPS and had his son removed from the home.
I don't know if its just me but it really makes me sick to think this kind of thing can happen with no evidence at all.