Pollito vs. polluelo
In the Spanish language, 'pollito' and 'polluelo' both refer to young birds, but they are used in slightly different contexts.
Pollito
'Pollito' specifically refers to a young chicken, usually still fluffy and not yet mature enough to be considered a hen or rooster.
El pollito amarillo sigue a su madre por todo el corral.
(The yellow chick follows its mother all around the yard.)
Mamá compró cinco pollitos para criarlos en nuestro patio trasero.
(Mom bought five chicks to raise in our backyard.)
Polluelo
'Polluelo' is a more general term that can refer to any young bird, not just chickens. It is often used in a broader context to include non-domesticated birds as well.
El polluelo de águila aún no ha aprendido a volar.
(The eagle chick has not yet learned to fly.)
Encontramos un polluelo de pato perdido cerca del lago.
(We found a lost duckling near the lake.)
Los polluelos de pingüino son alimentados por sus padres hasta que pueden cazar.
(Penguin chicks are fed by their parents until they can hunt.)
Summary
'Pollito' and 'polluelo' are both Spanish terms used to describe young birds. However, 'pollito' refers specifically to young chickens, while 'polluelo' has a broader application and can be used for any type of young bird.