Prep the pan: Heat the oven to 400°F (200°C). Line a baking sheet with parchment and lightly brush with olive oil to prevent sticking.
Soak the crumbs: In a large bowl, mix the breadcrumbs and milk.
Let sit 2–3 minutes until the mixture looks fluffy. This step helps keep the meatballs soft.
Add flavor and moisture: Stir in the egg, grated onion (and its juices), carrot, garlic, parsley, salt, pepper, and 1 tablespoon olive oil. Mix until combined.
Add the chicken: Gently fold in the ground chicken just until everything is evenly mixed. Do not overwork the mixture or the meatballs can turn dense.
Shape: With damp hands or a small scoop, form 1- to 1.5-inch balls (about 1 tablespoon each).
Place on the prepared sheet, leaving a little space between them.
Bake: Bake for 12–15 minutes, until the centers are cooked through. For very small meatballs, start checking at 10–12 minutes. Internal temp should read 165°F (74°C).
Optional golden finish: For light browning, broil on high for 1–2 minutes at the end.
Watch closely.
Rest and serve: Let them sit for 3–5 minutes to lock in juices. Serve warm, cut in halves or quarters for younger toddlers as needed.