What evidence in Frankenstein supports the thesis that the creature is an innocent child needing a role model or companion?
One of the best places that portrays Frankenstein's monster as an innocent child longing for love is actually, ironically, just after the monster murders Frankenstein's brother William, which Justine is accused of, tried for, and sentenced to death for. In Chapter 10, Frankenstein, so distraught that he goes traveling to and wandering through the valley of Chamounix, encounters the monster. It is during this encounter that the monster pleads his innocence and also begs for a companion. The monster's argument is that, because Frankenstein is his creator and has abandoned him, any guilt from the monster's wrongdoings actually rests on Frankenstein's shoulders. The monster argues that he has suffered due to his creator's abandonment, and it is due to his misery that the monster has been driven to do loathsome things. He further states that, his soul was full of love for life and humanity, but his creator's abandonment made him miserable, and misery led to desperate measures, as we see in the monster's grievous plea:
Believe me, Frankenstein: I was benevolent; my soul glowed with love and humanity: but am I not alone, miserably alone? (Ch. 10)
Hence, we clearly see that it is the monster's loneliness due to abandonment that has broken his heart and driven him to do despicable things. We further see a clear statement that the monster needs a companion when the monster reminds Frankenstein he has the ability to make the monster a companion, which is what the monster declares Frankenstein absolutely must do to put the monster out of his misery. We see the monster petitioning Frankenstein to make him a companion at the very end of Chapter 16, just after the monster has spent the last 6 chapters accounting the story of his birth, his experiences after being abandoned by his creator, what he'd learned from his observations of the French family in the cottage, especially what he'd learned about love, and his realization that he was a monster.
We also see in Chapter 11 just how the monster can be likened to a new born baby. In Chapter 11, he describes how he was overwhelmed by the newness of his senses, just like a baby would be overwhelmed. He also says it took him a while to learn how to tell his senses apart and to use them each individually, just like a new born baby would have to learn how to distinguish and use its senses.