The Prime Minister posed for photos with visitors at the WWT Arundel Wetland Centre this afternoon.
"When I turned up, the little one was trying to launch herself into the lake," she said. "I had my phone in my hand and then a security guard said to me can I not take photos.
"I didn't know what it was about. Then I suddenly realised the Prime Minister was there.
"I didn't realise who it was at first, as I was dealing with the children."
Boris Johnson took his children on a boat ride before offering to take a picture with Kim and her daughters.
Kim, from Salvington, said: "His wife took the photos for us.
"Their little one and Abby played for a couple of minutes while I was talking to them.
"They said they haven't been to the wetland centre before. They said it was really nice and they didn't know it was even here.
"They said it was really nice to get a bit of time away and have some quiet time.
"It was the most random thing, it was so surreal."
Click here to find out more about the Arundel Wetland Centre.