Watermelon/fruit shaped like a cake
https://www.ambitiouskitchen.com/smash-cake-recipe/
https://www.yummytoddlerfood.com/best-smash-cake-with-yogurt-frosting/
https://www.ambitiouskitchen.com/smash-cake-recipe/ we did this one also, and have made it since as muffins with smashed blueberries to have for snacks through week
for icing I just did coconut cream, cold, beat with a splash of vanilla extract and raspberries mixed in.
I didnt find any recipes that I felt comfortable with so I started researching non-food alternatives. We had him do a painting but I ended up giving him unsweetened coconut yogurt with berries. He had not had any processed food before then. Doesnt exactly answer your question, but I hope that helps.