Yellow
I'm not sure when Reagan learned how to pronounce her "L"s, but now she does it pretty well. For the longest time, they would come out like "Y"s, so for the word "yellow", she would always say "yeh-yo". Now that the "L"s are sounding perfect, she's changing too many "Y"s to "L"s. "Yellow" always sounds like "Lellow" now. This is the last bit of mispronunciation she still has, and it's too cute to correct.