Hi Katie,
Thank you so much for visiting the Disney Parks Moms Panel with your question. When my daughter was little, she loved the Disney Junior characters - and the place to meet them is at
Disney's Hollywood Studios.
At Disney's Hollywood Studios, your little one can
meet characters from Disney Junior such as Doc McStuffins, Sofia the First, and Jake the Never Land Pirate. Another fun and nearby attraction is
Disney Junior - Live on Stage! where little ones can dance and sing along to an energetic show featuring some of their Disney Junior favorites. A final thought for you is to try Play 'n Dine at
Hollywood & Vine, also located in Disney's Hollywood Studios. This joyful character meal gives children the opportunity to have a delicious meal as well as meet, dance, and sing with Disney Junior characters! Since you mention that you are going in mid-September, please do be aware that as of that time, the Play 'n Dine experience will only be offered at breakfast. See the link I provided for more information. Please do note that all character appearances are subject to change.
I hope that these thoughts are helpful for you, Katie! Have a wonderful time planning your magical vacation, and please do let us know if you have any further questions.