I hear you. We finally switched from rear-facing to front facing at 19 months, and 18 and a half pounds with diaper. Because, er, her sister needed the rear-facing seat to come home from the hospital in. We called it good enough.
She had like 10 different grunts that we called words at 2 years old, so she qualified for speech therapy four hours a month. Then, sometime around 33 months, suddenly she went from a whole 30 "words" (including grunts) over the process of 6 weeks to 20 word paragraphs that were gramatically correct including proper pronoun choice and verb tense. The speech therapist was shocked. I wasn't. You can bet that I was frustrated with her, and her with herself all the way up until that point. Her sister on the other hand... (rolls eyes upward), I had no idea that not yet 2 year olds could talk in spontaneous and comprehensible 7 word sentences. Quite a difference from 10 different grunts at the same age that her sister had. Aarghh!! I hope yours learns to talk soon. Go talk with early intervention and at least get an assessment.
I don't have 10 pounds to give her at the moment, but I'd love to take your generous offer of 6 pounds of your fat and painlessly stick them on her so that she'll hit what she's supposed to weigh for her age. Hey! We're finally back up and sticking to the 3rd percentile! <small victories require rejoicing>. We'll probably talk to the pedi at 4 years old and ask about the underweight booster seat thing too. If she continues to follow her curve, she'll be 28 pounds by then.
The biggest problem in my household, is that her sister is now into 2T clothing. And... the older sister remembers it and still wears some of it. I was hoping the fighting over clothing would wait until teenagehood, but alas, it is not to be.
This too shall pass. Quickly.