The reason you may be having trouble is that it often sounds awkward to have two consecutive adverbs in a sentence. Also, it is often awkward to have two adverbs modifying the same verb, no matter where they are placed in the sentence.
So in your example, it doesn't matter if you put the "deliberately" before "physically" or at the end of the sentence. Either way it's going to sound clunky.
I recommend instead you rewrite the sentence to avoid using "deliberately physically". For example:
Physical abuse is when someone deliberately causes physical harm or injury to a child.
Physical abuse is when someone causes deliberate, physical harm or injury to a child.
This sentence can be further improved by picking either "harm" or "injury" but not both, since they mean much the same thing. Also, in this context "intentional" sounds better to me than "deliberate".
Physical abuse is defined as causing a child intentional, physical harm.