Depends on your daughter, really.
My son's 5, and we just got back from our most recent trip. He'd collected a few pins on our last trips, but this was the first time he wanted to trade. Before we went, I explained that some people liked to trade pins they already had for new pins at Disney World, and that any person who worked for Disney and had pins displayed would probably be happy to make a trade. He pulled a few of his pins aside to be his trading pile, and I packed them for the trip.
Instead of the lanyard, which can be heavy for small kids and makes it easy to lose pins if the backs slip off, I carried the pins for him in a little container (a 4x6 photo case, actually) in my bag. When we approached a CM who was wearing a lanyard, he'd typically ask to take a closer look. It gave him an "in" for chatting with the CMs, but then, he's a very friendly, outgoing kid to begin with. When he felt a bit more shy, I obviously didn't push him to suggest a trade, but he mostly walked up and chatted about pins without any shyness at all.
If your daughter's really shy and afraid to approach new people, pin trading is likely not for her at this age. But if she's outgoing and chatty, this could be a fun way to interact.
