I noticed that my daughter sleeps longer when she sleeps on her tummy. She does not get easily interrupted when sleep in this position. I also noticed that in this position, she gets to exercise her body especially if she already wants to be carried. Unlike my eldest who could not lift her head when in this position during the same age, my second can already move her head from left to right and vice versa. I think in this position her locomotor will develop faster.
During day time, I allow her to sleep in this position. But not during the night because I’m afraid that she may not be able to breathe when her position covers her air passage. I could not still trust her ability to move her head by herself. According to our pastor’s wife, who was a nurse in the US for more than 30 years, this is the usual cause of Sudden Infant Death Syndrome there before. This also the reason why it is parents are discouraged to put the baby on this position when sleeping at night. I don’t want to take the risk. Probably, when she’s a little older.