“Huwag” and “hindi” are the words we use to mean “no” or “not”. “Huwag” is what we use to prohibit/prevent/disallow something from happening. “Hindi’, on the other hand, is used to contradict or deny something.
When used in the imperative with a verb, “huwag” then translates to “do not”. However, when it is not associated with a verb, it only means “not”.
HUWAG kang MATULOG dito. = DO NOT SLEEP here.
Doon ka matulog, HUWAG DITO. = Sleep over there, NOT HERE.
It shows that “huwag” does not always translate to “do not” and as such, it does not behave like the English auxiliary verb “do (not)” when used in the imperative, i.e., to be followed by the infinitive of the verb without “to”.
The Tagalog “huwag” may be followed by a verb conjugation depending on the meaning it is meant to convey.
Using the verb “bumitaw” as the example, we can use “bumitaw (infinitive/imperative)”, “bumibitaw”, or “bibitaw” after “huwag”.
Huwag kang BUMIT
ÁW = Don’t let go. - Use this when someone is holding on to you or to something at the moment. The command is only about that particular moment.
Huwag kang BUM
ÍBITAW = Don’t let go (this time, unlike the other times that you did). - The command gives an implicit reference to a similar situation (or situations) in the past to make sure that it does not happen this time.
Huwag kang B
ÍBITAW = Don’t let go (ever or as long as necessary). - The command is prospective.
Since “ 'pag nahulog, nakahawak ako, 'wag ka lang bibitaw (when you fall, I’m holding on to you, just don’t let go)” is a situation that might only happen, then the use of “bibitaw” instead of “bumitaw” is correct.