If in doubt, ask the flight attendant. The comon misconception that leaning forward and placing your head against a stationary object is unsafe probably comes from motor vehicle travel. Sitting upright in an accident is approved behaviour in a motor vehicle, however it is unsuitable for air travel because of the lack of shoulder harnesses and airbags in aircraft. An unrestrained infant cannot be held safely in many accidents. The safest crash position for an unrestrained infant being held is for the adult to be bent forward and the infant be held on the adult's lap.
Some positions are safer, at least for the adult, than others.
For information on child restraint systems, see our section on Travelling with children - Seating. If you are unsure about anything, ask one of the flight attendants. Decompression Pull oxygen mask toward you to start oxygen flow. Put your oxygen mask on as quickly as possible. Help children and others with their masks only after yours is secure.