Babies commonly regurgitate a bit of their feed and some make more of a mess of the living room carpet than others. The lower part of their oesophagus (food pipe) is not very good at preventing their milk refluxing back up towards their mouth again. It gets better over time and most babies have grown out of it by 12 months. Health professionals call this habit gastro-oesophageal reflux (GOR) and when it leads to troublesome symptoms such as pain, breathing problems or failure to gain adequate weight then we refer to it as gastro-oesophageal reflux disease (GORD).
It can be very distressing for families and there is no one magic cure. If you are bottle feeding, you could check that you are not overfeeding your baby; take a look at http://www.babycentre.co.uk/baby/formula/howmuchmilk/ for more information. We often advise raising the head of the cot a little to try to use gravity to keep the milk in the stomach and moving in a downward direction but, to be honest, the evidence for positioning having an effect on the severity of GOR is pretty poor. Your GP or paediatrician might prescribe feed thickeners or one of a range of different medications. You should always discuss the risks and benefits of any medications your child is taking with their doctor.