One of the most important things about cycling is that I get to do it as a family. After trawling the Internet, I came to the conclusion that fellow local cyclist Matt Chia has found a reasonable solution. I first read it on an older post but he has an updated one you can check out here.
Fixing up is easy and quick, 5 mins max. All you need is an allen key. This is how / where you attach the clamp to the seatpost.
Then you slot in the seat rails.
My wife rides the Brompton, me and son on the Dahon.
Making bubbles in the park.
The child seat is a Bellelli which I purchased from My Bike Shop. It is rated to carry a child up to 22 kg.