0-3 Months: Smiling at familiar faces, cooing, and visually tracking objects. 4-6 Months: Rolling over, babbling, and reaching for objects. 7-9 Months: Sitting without support, responding to their name, and playing peek-a-boo. 10-12 Months: Crawling, standing with support, and saying simple words like "mama" or "dada".
