So here's what I did.
1. Fill your sink with hot soapy water. Mix thoroughly to distribute the soap through the hot water.
2. Remove the lid from the cup and try to get as much mold as possible from the inside of the cup.
3. Place the cup and the lid into the soapy water and allow the lid and cup to soak for at least 5 minutes.
4. Scrub the inside and outside of the cup with a sponge. Allow the lid to soak. Focus on all the areas of the cup, in this case, the inside of the silicone stopper which may be difficult to get too. Grab a Q-tip to help get into the small hole. Return the cup to the water.
5. Scrub the accessible parts of the lid with the sponge. You can use another Q-tip to clean any areas you cant fit into and then rinse the lid thoroughly in the soapy water.
6. Once the lid and cup parts are scrubbed, take them out and rinse with cool water. Once finished and all the soap is gone, place them on a drying rack to dry for the remainder of the day or overnight.
I'm doing this from now on with these cups and also putting all 3 parts in the dishwasher once she's finished with her cup. Parenting isn't always easy and these are just life lesson to now be more aware of. Have you ever dealt with this before?