Some pearls are more precious than others, and I wish someone would have shared their “pearls of wisdom” and warned me about the great toddler travelling experience.  I would say this would apply to children as they begin to speak (cry and scream) and walk a little, maybe 1.5 to 3.5 years old.

If you can avoid travelling with such “gentle” souls, please do so.  Having said that the upside is you not putting your travelling life on hold for a good 2-3 years; those are valuable memories-making years.  Just remember that each child is different and yours might be a natural adaptive and easy going kid that goes with the flow.  Odds are not very positive on that end so if you don’t relate to that previous statement, maybe keep in mind the following:

1. Suds, Suds, and more Suds: Clothes detergent!  A sample size of course not the mammoth sized box, you can fill a Ziploc with it, but if you do try to get one with specs of colour so that it doesn’t get second looks (a la cocaine).  I was guilty of not bringing this, particularly if you are in short term stays in hotels, they typically require two days to do your laundry, and they charge you crazy money, cheaper and easier to just bring your own.  You will use it my friend – guaranteed.  Plus, saves you from bringing 5 sets of clothes.
2. Entertainment: Yes, you want them to appreciate the journey with you – they mostly won’t.  It’s unfair to expect them to be entertained in a museum, or site seeing.  Certainly won’t be if you do some shopping.  Obviously the entertainment will depend on your child – and your values.  If you are willing to do iPAD or DVD player, go for it.  For those who don’t you can ring colouring books, but I find those don’t work as well; think like small ball mazes, or things that move and make a little sound.  I’m usually in between the two options and I purposely don’t bring a charger so that when the iPad is done (usually half charged anyway) he uses other things.  Of course there will be time to amuse him with things in your actual vacation (i.e. zoo or play areas) but there will be some long car rides if you don’t have back up.
3. It’s their vacation too: The last point is a great Segway to this…. make time in the itinerary for them.  It’s unfair to make it all about you, but depending on how strong is your kid’s tolerance work intermittently playground time, a swim, any park time, a zoo or a play area if there is one.  Just having them run and scream is always a guaranteed good time for them.  You’ll have to work on your itinerary to include those things without wasting time going back and forth as much as possible.  That way you’re not frustrated.
4. Food provisions: In many places, especially Asia, cutlery is not available (they’ll have chopsticks for kids though).  In Europe they will have adult cutlery, and rarely a small cup for kids.  So don’t forget to bring those plastic forks and BPA free bottles; especially since they’ll surprise you with how often they need water.  On that same wavelength, equally surprising how they want food in the most inopportune time.  Pack up snacks, better if they are packaged or Ziploc’ed and separated, and if you run out – see if the hotel breakfast buffet will have some croissants you can bag in or those cheese and crackers.  Those little nut bags on the plane come in handy – if you can resist not eating them yourself while flying!
5. Blanket and Neck pillow:  Always get a blanket (preferably a “Blanky” if they have one) they’ll need that false sense of comfort when they’re in the stroller (if not then they are light enough to carry around).  Neck pillows are also very useful when they go to sleep and saves you from their whining from waking up sore later.  If your kid is a deep sleeper, take advantage and go out for some city strolls or local restaurants while they are catching up on their zzz’s with their blanket and neck rest.
6. Stroller/car seat: Goes without saying a car seat is a must (even if it’s not legally required in the country you visit), if you’re not expecting long journeys, you may consider leaving it at home and just holding tight to them while they sit next to you – but I don’t recommend this at all.  I realise car seats can be crazy bulky to take with you; but sometimes hotels can help with giving you one at your destination, check early.  To be honest I didn’t use them when we were taking short cabs or quick trips, but if you get a driver, make sure they have one for those long journeys – you’ll be surprised how prepared they are in almost every country (their business depends on it).
7. Keep your timing loose:  Don’t be uptight in your trip schedule, you’ll inevitable do 80% of what you scheduled, kids will want bathroom time, when it’s the most inconvenient time to do so, get hungry or throw the random tantrums in the middle of the quietest place (so you’ll have to leave with what’s left of your self respect).  Be mentally prepared for this and make sure you have free days to catch up on some missed sight seeing another time.  It’ll relieve some of your stress on the trip and make you more pleasant to be around if you’re a control freak like me.