Bring a bike lock for the stroller. They are not welcome in many restaurants and some shops. Best to be prepared.
Check to make sure that restaurants are kid friendly before you visit. If there are no high chairs it is best to know up-front. Also kids and long lines do not mix. Make reservations for places you want to visit that have long wait times whenever possible.
Do not over plan! You need a plan with kids but it must have additional time in it for the inevitable issues that come up when traveling with kids.
Be flexible! (We once went to a restaurant for dinner only to find that they closed at 4pm! We had 2 hungry, cranky kids and we were 6 hours from home! We walked up the block to the first place that looked kid friendly. It turned into one of our favorite places.)
Pack their “special” item. It is a common tip to bring a small child’s lovey or blanket but nobody ever mentions the importance of bringing something for older kids. Your tweens and teens need their favorite items to feel secure on the road. Don’t forget their Ipod or DS! You want them to be comfortable as well.
Many hotels have crib rentals. It is often not only cheaper but more comforting for your child to bring a pack & play from home. I must stress this is only an option for car trips. Do not try to bring one in a plane!
Pack a spare. Bring a spare of all basics when kids are involved. Spare outfit, shoes (we once lost a shoe while strolling around), socks, toothbrush (new in the pack for whoever loses theirs along the way), and a memory card for the parents! Nothing like a full memory card to make you mad!
Do not let your kids eat drastically differently than they would at home. If you do not normally allow junk food and sweets than you must limit them when on vacation as well. Kids have sensitive little tummies (as do most adults!). When you change their diet to all fast food or way more sweets a day; you are asking for trouble! Nobody has a good time when part of the family does not feel well.
Consider how active your family is. I have no problem with active trips! We are a very active family. That being said: If your family or even one member of your family is inactive or very out of shape then taking them on a highly active trip may indeed be too much for them. Think of the whole group when picking out what to do. Also consider a child’s abilities. Even children can go hiking as long as you pick an appropiate place to take them.
Learn about the history or culture of a place before visiting. This helps to turn the trip into a learning experience like no other. Make sure to see one historical or cultural point that goes with what you have learned.