Make a big pile of everything you'll need, then cull it if you can. Leave plenty of time for re-packing - you'll probably need at least one 'trial pack' before your finally happy with your arrangements.

Check your airline baggage policy carefully before you begin. In particular check the weight, size and number of pieces restrictions for cabin baggage and for children’s fare passengers. 

How to avoid excess baggage fees --- here's good advice from magellans.com

Establish whether the bags and cases you own will give you maximum carrying space within these restrictions.

To keep your hands free in terminals, consider using a back pack as your principal piece of hand luggage. Label the pockets for easy reference when very tired!

Pack your cabin bag to include smaller named packs of toys, nappy changing things, spare clothing, wash bag, medical kit and emergency rations. This way you can re-apportion the hand baggage amongst yourselves if a check in assistant has a problem with the size of your cabin bag. It also helps with in-flight organisation.

Use a waist pack or similar for your passports, tickets and cash. You can put it away in the pack once onboard.

If you’re travelling with a baby, take a front pack in your cabin bag. This helps when moving around the plane, collecting luggage from the carousel and at any time when you’ve been separated from your stroller.

Consider taking a toddler back pack for an older child or the really versatile stroller backpack.

Definitely look into purchasing a Baby B'Air travel harness. This is the only harness we have seen which is specifially designed to keep a small child safe from air turbulence  whilst he sits securely fastened but able to move around in his parents lap.

Take only an umbrella folding lightweight stroller or car seat with detachable wheels to get the best chance of getting your buggy on board the plane. Don’t be surprised if it is taken from you at the departure gate to be placed in the hold.

Consider taking a set of reins or an elastic wrist/waist rein for toddlers. This way they can board the plane under their own steam, and enjoy a little freedom in the terminals whilst working off some energy.

Eagle Creek Pack-It cubes come in all shapes and sizes that are perfect for separating kids clothes and grown up clothes without little tiny socks getting swallowed up in the bag.  Sew patches on them from where you've been so they are a little more interesting.