The sentence requires the past participle form of the verb to function as an adjective describing Nehal's childhood.
Filled (Correct): When we say something was "filled with," we mean it was full of a particular quality or thing. Since the sentence refers to the past ("Growing up," "was"), the passive structure "was + past participle" is required.
Full: While "full" has a similar meaning, the correct prepositional phrase would be "full of," not "full with."
Filling: This is the continuous form (present participle). Saying a childhood "was filling" would imply the childhood itself was performing the action of filling something else, which is logically incorrect.
Fills: This is the simple present tense and cannot follow the auxiliary verb "was" in this context.