These children are called "karako" (唐子), which literally translate to "Chinese children". "Kara" (唐) is actually the character for the Tang dynasty (618-907) of China, considered by many as the golden age of Chinese culture and power. The little children design on pottery symbolizes health for sons & daughters and longevity/continuity.
The number of children on the design also have significance. You will probably see three, five or seven children. (Always odd, never even number!) The more children on the pottery, the higher is its grade.
This matcha tea bowl has 5 children...and the pine tree is found on the inside of the bowl!