Raise your fingers to another member and you'll receive a loss in return. You should never hurt a member of your team, group, or society. It's just wrong. And you'll incur a loss as punishment for your bad deeds.
Unfortunately for you, payment is in the form of the loss of your son (そん). The loss of any family member is horrible, but this was your son. He was your favorite child. You loved him. But that's the loss you must bear for raising your fingers to a team member.
Currently there are no similar looking kanji which exist in the WaniKani learning system