New mom Meghan used the occasion to swap parenting tips with other parents as she discussed Archie's sleep patterns, teething and crawling.
Thompson praised Meghan, saying, "she's just a normal mum and it was like talking to friend".
Mrs Herschel said she joked with Harry, who she met at the same event in 2018: "I told him a year ago he would have a boy then a girl and I'm right so far".
Baby Archie made his first official debut as a royal during the couple's 10-day tour of Africa, where he "found his voice" and was making more noise than ever before, according to his proud parents.
"Meghan promised not to tell anyone that I was off school", Molly said.
Andrea McMahon, the military unit's assistant regimental secretary, said: 'Poppie was hoping to get cuddles from them and we knew how much Harry loves children.
The following day, members of the royal family will attend a Remembrance Sunday service at The Cenotaph, the war memorial in London, in order to pay their respects.
In contrast, Meghan, 38, wrapped up warm in a thick wool coat for her engagement.
It was the Duke's seventh visit to the Field of Remembrance, having represented the Royal family at the event annually since 2013, but the first time that his wife has joined him.
The Duke and Duchess of Sussex dropped in on a parent and toddler coffee morning in their home town and spoke about how they would miss Archie if they had to spend long periods overseas without him.
Meghan previously wore the same boots on Christmas Day previous year, when the royal family attended a church service at Sandringham.
A Clarence House spokeswoman said: "The Duchess of Cornwall has been told by her doctor to cancel her engagements owing to a chest infection which has got progressively worse over the last few days".