When our son turned two a couple of years ago, it was time to book him his own seat on flights.
I had no idea that there were child restraint options other than the lap belt provided with the plane seat, until by chance I saw one advertised.
Here’s what I discovered...

Airlines generally require that children from the age of 2 years require their own separate seat. Aeroplane seats are large, and toddlers are small, so ensuring that they're seated safely requires the use of either a child restraint seat, or a child safety harness.  Child restraint systems are in most cases recommended for children up to 4 years of age, 18kg, or 100cm high.  After that, the standard aircraft seat may be more suitable.


Bringing a child car safety seat along for the flight is one option, and can work well if you need a car seat at your destination.
Airlines have different policies on what is and isn't allowed, but generally “booster” style car seats are not permitted, because they don't contain an in-built harness system.  Child restraint car seats designed for small children (up to four years of age), with their own harness system, are normally permitted to be taken on the plane for use. Checking with the actual airline beforehand is important, as different policies and restrictions apply, and some child restraint seats will be too large to fit on a standard aircraft seat.
The main drawback of using a car-style child restraint seat is that it is large and bulky to bring onto a plane, and fairly cumbersome to attach, particularly in the midst of boarding on a crowded plane.


A much easier option for securing small children, is the use of a specially-designed, aviation child restraint system.  
This can be purchased by parents prior to flying, and has the advantage of being highly portable, and straightforward to use.
These systems don't utilise a separate seat, but instead interface directly with the aircraft seat. 
Some airlines provide their own, which may be available for use by children on certain flights. 

                                                   Image care of Little Gulliver

                                                   Image care of Little Gulliver

The main product available to parents (and the one we use and recommend) is the “CARES” Child Safety Harness, produced by Kidsflysafe Inc.  CARES is designed for children between 1-4 years of age and fits into a small stuff sack, allowing it to be carried easily. 
This harness has been approved for aircraft seat use by the Federal Aviation Administration (FAA), and other global aviation authorities, such as CASA (Civil Aviation Safety Authority) in Australia.  The harness is sold throughout the world. 
Links to various retailers can be found on the Kidsflysafe website.

Some airlines may provide their own harnesses or custom child seats, which may be available for use by children on certain flights. 
An example is the “SkyKids Child Seat.”

I would recommend always checking with your chosen airline to see what options they provide.

Happy, Healthy Travels!

** Healthy Kids Travel has no affiliation with these products.