Abuse takes many forms, and sometimes parents abuse their children and don't know it.  Ignoring the child when it wants attention, or insulting it by telling it it is bad or stupid or some such thing, or teasing the child and embarrassing it in front of others, or relentless tickling or roughhousing when the child gives "enough" signals, or, of course, punishments that involve denial of food and such.  We can even abuse a child by failing to hug it or tell it you love it and will care for it.

That abused children often (more often than we care to admit) do the same to their children is an ongoing disaster.