Wiktionary
thumbsucking
n. The act of sucking one's thumb.
Usage examples of "thumbsucking".
I took with me five children ranging in age from my own newborn daughter and fifteenmonthold Yvain, to a twoyearold, thumbsucking girl and two fouryearolds, a boy and a girl.
Rahi shouted suddenly, as a housewife with a thumbsucking child in tow went by the stall.