The pumpkin was spirited away from the front porch of a property in LeDroit Park in Washington DC, which greatly upset the young boy, called Tommy, and left the parents feeling livid.
To shame the thief, 33-year-old stay-at-home mom Becky wrote a message for him or her on a piece of card and fixed it to the front of the porch.
Becky first posted the note on Facebook but when one of her friends posted it to Reddit her maternal outrage went viral.
The note read: To the person who stole my sons pumpkin. Thank you for the life lesson. This will help teach him that sometimes people are mean for no reason and you just have to brush it off. Because my son is two years old and cannot read this sign, I will add: You are an a******.
Becky, who also has a three-month-old daughter called Abigail, told MailOnline that her son, despite his young age, understood what had happened and was very upset.
She said: "I had already put up the sign to distract him from the loss of the pumpkin. He definitely understands what happened. We put them out last Sunday and every morning when we went out he would point to each and say Daddy pumpkin, Mommy pumpkin, Tommy pumpkin, Abby pumpkin."
'When I told him over lunch on Monday that more people like our sign and are sorry about his pumpkin, he started crying and saying "Tommy want Tommy pumpkin".
She added: "I was livid but recognized there was nothing I could really do to keep him from finding out only his was missing. So I wanted to distract him and shame the thief. They might never see the sign, but the thought made me feel a bit better."