What's the best Android app for tracking infant developmental leaps and understanding fussy phases?

The Wonder Weeks is an Android app designed to help parents monitor their infant's developmental leaps, which are predictable periods of mental growth often accompanied by increased fussiness. Based on child psychology research, the app charts these leaps from birth through the first 20 months, offering timelines that predict when fussy windows might occur. Key features include daily updates on a baby's leap progress, tailored activity recommendations to engage with developmental changes, and the ability to track multiple children in separate profiles. For real-world use, parents can reference the app when a baby becomes unusually clingy or irritable, gaining insight into potential cognitive shifts rather than attributing behavior to random causes. Reviews indicate that many users find it invaluable for maintaining patience and confidence during difficult phases, with one parent noting it 'helped me stay regulated and confident in my abilities.' However, the app has faced criticism for technical issues, such as past crashes and purchase restoration problems, though updates have often resolved these. The premium access cost, noted by some as steep, may also be a consideration. Despite occasional bugs, its structured approach to developmental tracking makes it a useful tool for new parents seeking to understand infant behavior patterns.