Linguists sometimes differentiate between active and passive bilinguals, the active ones speaking as well as understanding more than one language, the passive ones understanding a second language well enough but speaking in their own language. On that scale, our child could be classified as a passive monolingual. She understands a lot of words and expressions and social rituals but doesn't try to use the appropriate words very actively. She recognizes so many words that we are tempted to switch languages or spell things out sometimes so that we don't get her all keyed up to do something we're not ready to do immediately—like eat or go out for a walk. She gets confused by some near-rhymes, like hedge and head, tongue and thumb, knees and sneeze. She is most fond of d, t, j, and associated consonants, together with i, a, and u for vowels. So far, she hasn't pointed and labelled things for herself, only elicited labels from us or pointed at things we label. Her first "parroted" word was the sound of an owl she picked up from reading an animal book with the babysitter's daughter. Now when the mood strikes her, she runs to a picture-map of the zoo and points to the owl, saying "Hu! Hu!" But of course she's never attempted owl. The only real words she has tried to imitate are Jeep, juice, zoo, and one attempt at boo that came out pretty close to zoo.
Of course, adults don't usually sit around naming things at each other. There are other more appropriate social rituals that involve language. She is starting to master some of them. After months of observing us waving bye-bye to each other every morning for her benefit, she has finally figured out what it means and now waves bye-bye to parting friends and vehicles, to bushes whose flowers she has stopped and patted, and to the automatic money machine whose buttons she often stops to play with on the way to the babysitter. She has just begun to say "Hi" appropriately every once in a while, but never on demand. She recognizes yes/no questions addressed to her and often responds with a vigorous shake of the head. At other times, she responds to every question, statement, or command with "huh?"
UPDATE: This child is now a 24-year-old teacher in Boston Public Schools.