I lost those few kilos after my third baby as easily as my first and second, within weeks. I was a bit worried because I had a more obvious after baby belly than I did with the first 2 so I thought it may have been easier to shift but it wasn't. I didn't do anything new to lose those few kilos, I put 8kgs on with each pregnancy so only had 4-5kgs to lose after babies. I just got back into light weights and my long distance walking as soon as I felt ready too. I have a few friends who have problems losing the weight after their 3rd babies who are very fit so maybe it is common.