Meghan Markle and Prince Harry sent a reply to the tots at Preston's Little Rascals Nursery.
The children sent the royal couple a card back in May, congratulating them on the safe arrival of Prince Archie.
The nursery was surprised and delighted to receive a reply from the Duke and Duchess of Sussex.
Lisa Thompson, a staff member at Little Rascals, said the class - all around 16 months old - were "so excited" to read the letter.
"We have a few children whose mums were expecting babies," says Lisa, "so we have been doing a lot of activities and chatting about expecting babies.
"When I was working at a different nursery we sent one to the Queen on her birthday. I still have a reply letter from the Queen at home."
So when Prince Archie was born on May 6, 2019, and Lisa decided it would be exciting for the kids to send a card.
"We decorated it with hand paints and sent it the next week."
The card read: "Congratulations to the Duke and Duchess of Sussex on the safe arrival of baby Archie."
Then, on July 18, Little Rascals found a special letter in their mailbox.
The royals had sent an official photo of Prince Harry and Meghan Markle with the newborn Archie.
"They were all so excited," says Lisa, "the girls were pointing at the baby and saying "look at the baby".
"And the boys were really interested too - they were trying to say Archie's name".
On the reverse side of the photo, a message read: "The Duke and Duchess of Sussex greatly appreciate you taking the time to celebrate the birth of baby Archie Mountbatten Windsor".
"It was fantastic for the kids," says Lisa, "I think we'll definitely send more letters on special occasions from now on".