Explore the topic of cute names to call your girlfriend
This is a good place to start since childhood particularly inspires fun and innocence. Toys, cartoon characters you used to watch and other childhood fun stuff are where you can find such cute names. Then there is your memorable times category. Now this is easy because you will simply have to remember a particularly lovely time together and take inspiration from there. For example, if you went to the park and she kept looking and touching the flowers, you can call her bumble bee.