infancy
穉 centers on the earliest stage of life: infancy, the state of being very young or immature.
穉 combines 禾 (grain) with 犀, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with young grain or infancy.
The left side 禾 suggests young grain plants, and the right side 犀 looks like a sturdy animal. Picture a tiny seedling beside a large rhino, emphasizing the idea of infancy and small beginnings.
For チ, imagine a tiny infant drinking tea: tea -> チ, and the small cup matches the kanji's meaning of infancy.