1. Rinse the millet thoroughly under cold water.
2. Cook the millet according to the package instructions. Usually, this involves boiling it in twice the amount of water (for 50 grams of millet, use 100 ml of water). Let it simmer on low heat for about 15-20 minutes, or until the water is absorbed and the millet is soft. Allow it to cool completely.
3. While the millet is cooking, wash, peel, and core the apple. Cut the apple into very small, baby-friendly bite-sized pieces.
4. In a large mixing bowl, combine the cooled millet, apple pieces, and peanut butter. Mix until all the ingredients are evenly distributed.
5. Once well-mixed, shape the mixture into small bite-sized balls suitable for your baby's grasp.
6. Place the bite-sized balls on a plate and refrigerate for 30 minutes to help them firm up.

Summary:
This snack is excellent for babies as it's filled with nutrition. Apples provide essential vitamins and fiber, millet is a good source of protein and iron, and peanut butter adds healthy fats and additional protein. These ingredients foster development and growth while introducing your baby to varied textures, promoting motor skills development through baby-led weaning.

Storing Options:
The bites can be stored in an airtight container in the refrigerator for up to 3 days. For longer storage, place them in a freezer-safe container and freeze for up to a month.

Possible Side Effects/Allergies:
Peanut butter can be a common allergen for some babies. Introduce it in small amounts and keep an eye on any allergic reactions such as hives, swelling, or difficulty breathing. If any allergic reaction is observed, seek medical attention immediately. Always consult your pediatrician before introducing new foods to your baby's diet.