We absolutely loved our stay in Marleen's accommodation! I stayed there with my wife and our 2 kids (6 & 3). The apartment itself was very spacious and clean. Our kids loved having a variety of beds to choose from, and we especially loved having 2 sinks in the bathroom! Beds were comfy, storage space plentiful, cold fridge, filter coffee machine, consistent wifi and good hot shower all included! We also appreciated having the balcony space to chill out on in the evenings with a beer after the kids were asleep. Our only minor quibble with the accommodation would be that a clothes washing machine would be very useful for guests. We knew of course upon booking that there wasn't one but underestimated how quickly our kids would go through their clothes during our stay (packed very light and misjudged quite how many playgrounds Berlin would have on practically each corner!).
Moabit itself is a chilled out residential area, with the U-Birkenstraße station literally a few steps away in front of the building...particularly grateful for that after long days out with the kids! The supermarket is also a short walk down the street, as are several playgrounds around the corner. We'd recommend across the road Lichtblick for their delicious salads, and also a 20min walk away is an amazing Lebanese/ Persian restaurant called El Reda! It wasn't difficult to travel from Moabit to elsewhere in Berlin, particularly useful to have close by was Berlin Zoo and Tiergarten.
The last thing I would say too was that Marleen was a great host. She was very responsive before/ after our booking with clear check-in information. After we had a minor query about the TV she resolved it the following morning, our kids were very happy to watch german cartoons after a busy day!