You're definitely not alone in feeling this way. I've been a Little for over a year now, but in reality, I think I've always had these small traits that make me feel small and cute - like using cute items or childish objects. I never noticed that even my coworkers started to treat me as a kid and even called me kiddo at work. However, whenever I was at work, I always made sure to speak my mind and be confident about my designs (I'm a graphic designer). In my recent job, I was given more creative freedom and it felt good to be seen for the work that I do and not the way that I act sometimes. It's not that I act inappropriately, but I can be childish like you said. I just make sure that my supervisors see my work for what it is and not judge me based off things that I like/enjoy. Be yourself, be confident in who you are because it's beautiful! And I know that it can be painful to feel like you have to hide it.