Perhaps the book explains this better than the movie, but why was Claudia helpless? Why did she need a protector in Interview With The Vampire?
"It's forbidden to make one so young... so helpless... that cannot survive on its own."
We are made to understand earlier in the movie that she is unable to create vampires, so we know this is one limitation of her size. Claudia says something to the effect of "I suppose we could people the world with vampires, the 3 of us" and Lestat replies, "Oh, not you, my little Claudia". For this reason alone, Claudia is less powerful than a vampire made from an adult.
Nevertheless, Claudia's mind grows as normal - and she is intelligent and capable in the movie. She participates in detailed ruses to lure in her human prey, and concocts a plan to destroy Lestat by feeding him dead blood. Indeed, she even cuts his throat herself. We see in several scenes that she is more than capable against humans (I suspect any vampire would be, adult size or not).
So when Armand says she is helpless, and cannot survive on her own, what does he mean? I realize she would have more trouble navigating the world than an adult vampire, as all the humans would initially treat her as her child appearance. But as far as pure survival, she seems as though she would be able to do so without issue. She would never have progeny, but survival alone, she seems fine.
It would seem her other large failing is that she is unable to defend herself against other vampires -- but neither can Louis when they are outnumbered 15 to 2. So what does Armand mean?
(As a side note, does Claudia still grow more powerful with age, as the vampires made from adults do?)