Hi Dr We have twins of 6 months old giving formula milk till now we were feeding with pigeons bottles from 3 months now we have change nipple for 6 months Nipple which is Y cut but suddenly their are very slow in feeding taking more then 1 hr for drinking 120 to 150 ML so we again started giving with old 4 months nipple they are comfortable with them ... As they are now more than 6 months so we changed bottle to philiphs Avent Natural 6 months.... but they are drinking only 30 ML not more then ... what should we do ...??????