We can use the word "play" to mean that something is acted or done for fun. It means that it is not real. For example we can say:
The kids went play fishing, using sticks and string and pretended to catch everything from a sardine to a whale.
Similarly you could say "They are play fighting" to mean they are pretending to fight. There could be other childish expressions like "bundling".
On the other hand, if the intent is to annoy, then I would just use "hit", "punch" or "kick" etc. modified by "not very hard" or similar:
Callum punched his sister. I know he didn't do it very hard, and was just trying to annoy her. Still, his punishment is to lose his phone for the next hour.
Another word is "Spar" which means the practice fighting that boxers do to train, and figuratively "sparring" is fighting for practice, not to win. A boxer who is not hitting as hard as he can is said to be "pulling his punches". Metaphorically this is often used in the negative: "He isn't pulling his punches" means he is fighting (or arguing) as hard as he can.