The Spanish word 'pipi' comes from 'pi', which is an onomatopoeia (a word that imitates a sound) representing the chirping of birds. This is a common pattern in child-directed language, where animal names are often derived from the sounds they make. The word was likely doubled to create the diminutive, child-friendly form 'pipi', making it easier for young children to say and remember when referring to small birds.

The simple sound 'pi' is still used in Spanish to represent bird chirping, similar to how English speakers might use 'tweet' or 'chirp'. This onomatopoeia forms the basis for the child-language word 'pipi'.

While there aren't direct English cognates, English also uses bird-sound onomatopoeia to create child-friendly bird names, like 'peep' (as in 'baby chick') or 'tweet-tweet'. This shows how different languages often use similar patterns in creating words for children.