Pequeño or pequeña, depending on whether the subject is masculine of feminime.
Es joven (little/young) Es pequeno/a (little/small) (tilde, the little wave, on the 'n') (male/female)
pequeña pequenita (with ~ over the 'n') if she's very small
The Spanish word for 'little piggy' is 'cochinito'.
This is a little dependent on locality - the term for "bra" changes depending on where you are. One way to say this is "sujetador pequeño anaranjado."
poco
'Your little sister' in spanish is written and pronounced 'Tu hermana pequena'.
You can say "Eres pequeño/pequeña".
perrito
un poco
Campanilla
Poquito or poco.
Besitos