As I'm packing for a weekend trip, I realized we're starting - slowly - to move into the easier part of traveling with children. It's all a function of feeding and sleeping, regardless of age. My ranking on age vs. ease of travel is:
1. 0 - 4 months is the absolutely easiest, if the child is exclusively breastfed. Babies this small sleep anywhere at any time. They're completely clueless to where you are - and really don't care as long as you can take 20 minutes to sit and feed them or hug them close in a baby carrier for sleeping.
2. 2.5+ years comes next. For us, at least, after William was this big, his naps became very predictable. Food isn't an issue (assuming no allergies!) as the kid can eat all table food. So, just make sure to be at the hotel from 1 - 3:30, and all is good to go.
3. 1 - 2.5 years. Food is mostly not a problem (baby has graduated to table food and milk and juice). Nap time can be tricky because sometimes the toddlers like two naps (terrible for sightseeing!) and sometimes one - and sometimes none and they're cranky all day. But, if you're able to navigate the nap time issues, because the toddler is usually walking, it's easy for him to burn off that endless child-energy.
4. 4 months - 1 year. This is the absolute hardest time, in my opinion. The baby is wanting to crawl (yes, I know, 4 months is not a normal crawling age ... but this is what I was dealt with both boys), but floors when traveling are often less than clean - even if you're not in India. Food can be difficult since you have to pack baby food, figure out where to buy it, or constantly ask if a restaurant can puree things (though I've read of some beach resorts which are starting to stock it!). Plus, the baby is only just being introduced to foods (and traveling is not a time you want to discover a food allergy), so food options are limited.
The good news is, Patrick is out of Phase 4. We did pack some rice cereal, remaining baby food tubs, and a little formula - but mostly for comfort than necessity. He's walking (and looks so cute in William's old Crocs!), so our concerns about cleanliness are lessening. He's usually at one nap, and unlike William goes to sleep easily, so Phase 3 should be simpler with him than William.
I'm not 100% sure yet ... but it seems to me after eight years old traveling with the boys will seem like a piece of cake. At least, that's how old Beth was when I moved to Japan -- and I remember the two of us being pretty self sufficient on the planes. Hopefully William and Patch will take after us!