I have both actually - I would suggest the Havana Hobo for you.
Nico has a bigger size, but the bag sits at your bum area (where your hand is if you put your hands down) after you put it over your shoulder, and I think as a mom with 3 small ones, when you want to hold hands with your kid the bag would be in the way (or if you need to carry other bags and such, it would be less convenient) - not to mention the part of the strap that goes on your shoulder is rolled, so if your bag gets heavier, it might cut into your shoulder - I don't have the problem, but my mom tried my Nico and she said it was hurting her cuz the strap would cut into her shoulder.
The Havana however is smaller, but it is still pretty big, so it should fit your everyday things for your kids (unless you carry a lot, then I would recommed the Nico again). After you put the bag on your shoulder it sits at the torso area, so it would leave your hands "free" so to speak (am I making any sense here?). Not to mention, the strap on the Havana is flat, so even if you put more things in the bag, the strap will not cut into your shoulder and it would be relatively more comfortable.
One thing I have to warn you however, is that the Nico has a zipper closer and the Havana dosen't - so you have to make sure you close the magnetic closure and make sure your flap is properly placed down on your havana.
Hope this helps!