This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 孨 is uncertain. It visually contains three 子 (child) elements, but the original meaning and component relationships are unclear.
Three children (子) stacked together: the top child and the doubled children below. Without a clear meaning, picture a rare, mysterious character made of three kids.
For セン, imagine three children sending (セン) a secret message: send -> セン, and the three 子 kids are the messengers.