Turn it around
…there’s the same difference between spanking and beating (abuse); as there is between timeout and locking a child in a closet/box/basement (abuse); as there is between telling a child to go play outside, and leaving them outside to suffer/sicken in the snow/rain/heat (abuse); as there is by skipping a meal in prep for a feast or because sleep is more necessary, and not bothering to feed them (neglect) or regularly refusing them food whilst everyone else eats (abuse); as there is between cuffing them upside the head in affection or ‘Oy!, and boxing their ears/punching them in the head (abuse); etc.
Striking someone? Is like sex v. rape. Exact same physical action… WILDLY different events.
People -both kids/adults- can be hit with affection and smiles/laughter on all parts, to get someone’s attention, as instruction, as discipline, as a trial/hazing, as punishment, in anger/rage, &/or abusively. Prolly not a complete list… just sorta off the top of my head sliding along the scale.
Ditto physical violence that leaves huge marks (bruises, scars, broken bones) can be somehing cheerfully entered into and proudly displayed (think sports), whilst something that doesn’t even redden (like a pinch, or grabbing someone up by the hair) can be cruel as f*ck.
How to tell what’s what? Context.