Weight limits are a really hard thing to judge for manufacturers, especially when it comes to cargo as the weight distribution can vary so much. Often, the frame can be super solid and tested for high weights, but unless you find a reliable supplier of a fork that can take the braking loads of 200kg low-slung mass then you have to reduce the approved weight of the whole bike. Same applies to stem, handlebar etc etc. Same with racks, the tests are quite harsh, so speccing a weight over 25kg and taking responsibility if a kid is injured is a huge liability most companies aren't willing to take on.
In almost all cases, if you ride the bike sensibly then you can get away with a much higher weight than the specs allow. I've seen 4 grown men on a bucket style cargo bike and it held up just fine. I believe R&M started with a kids 20" Suntour fork on the front of their bike, Suntour have updated it to be Cargo ready now, but I haven't heard any reports of the original ones being a danger in reality.
Take a look at the Bergamont Cargo models, they do an LT which is similar to that Multicharge.