Infant lifejackets will almost certainly have been onboard although in any airline I have worked with they have not been given out to parents unless it is a premeditated ditching.They are stowed in a locker with other emergency equitment. Unless they knew they were ditching I would have thought it unlikely the child was wearing an INFANT lifejacket. The parent may have made the decision to put an adult lifejacket on the child and depending on age/size of the child it may have been ok. Adult lifejackets can be used on a child by inflating before ditching and then deflating it slighty and tieing the tapes acroos the chest and then behind the childs back.
Nothing short of a miracle that the child survived. Very sad indeed the loss of another aircraft regardless of where the plane was from and nationalities onboard.