My DD is also small/petite. I have noticed that because of her size, bigger kids tend to treat her like a 'baby', ie - pick her up, try to do things for her, basically try to cater her. Have you ever seen that movie Simon Birch? The scene when all the kids take turns picking him up and carrying him, remind me of what my DD goes thru LOL!
I have reminded the other children that she is older and not to pick her up with out asking her first. For the most part, I feel that she needs to learn how to fend for herself, so I leave it up to her. If she asks for my help, then I do my best to help.
She has learned. She is very loud and direct with what she wants and what is okay or not okay with her. She does tend to be a bit bossy, but I think that stems from needing to be, not so much personality KWIM?
Right now, it seems our biggest problem is other adults. They look at her and see a 3 or 4 yo, not a 6 yo. When they see how she behaves and how well-spoken she is, they tend to get upset that their 3or 4 yo aren't like that. They try to use my DD as an example. I have to remind them that she is 6 yo, and that their children are fine.
Well, just my input, hope some of it helps or even just lets you know you are not alone.