Zara and Mike seemed in good spirits on the occasion, sharing a smile as they pushed their new family addition around the park.
The pair wore matching blue tops whole Mia wore a soft pink anorak, with her blonde hair tied in a little ponytail.
At one point Mia could be seen playing with Isla Phillips, five, who is the Queen’s great-granddaughter.
Isla’s parents are Peter and Autumn Phillips.
Peter was the first of the Queen’s grandchildren to marry and the couple welcomed a baby girl Savannah in 2010.
Isla arrived a year and a half later.
Meanwhile, Mia’s sister Lena Elizabeth Tindall is the newest addition to the royal family and is 19th in line for the throne.
Zara Phillips recently made headlines in the UK, over her candid account of Prince Harry and Meghan Markle’s wedding – describing it as ‘uncomfortable’.
Zara – who was pregnant at the time and famously made some unimpressed facial expressions during the lengthy service - explained the seats weren't very wide – which caused her some issues.
‘My bum sort of slid over either side and Lena kicked the hell out of me for an hour. It just wasn't comfy at all and it probably showed on my face,’ Zara told the UK’s Daily Telegraph.
‘It was just the general amount of time everything was taking. I think my face was probably caught at the point when I thought: 'Right, he's going to finish now', and then he went off on another little story, and it was like, 'Really?.’