I wish I could be more help, but I started Layla off very young with it. As long as her hair was long enough to put a little clip in, she had something in her hair every day. She hated it at first and tried to get it out, but eventually she got used to it and now prefers being able to see
Maybe you could start out with just using plastic barrettes or something and then distracting them with toys or treats, and be consistent with that every day? You could start off just putting them in for a 5 minutes, then 10 or 15, and eventually get them used to wearing them all day