Research, research, research
I can not stress this enough. When ever you plan a trip whether at home or abroad take some time to read up on your destination. Find out what is there to see and do, what is the climate and weather forecast, and how much will things cost. When planning our trip to Rome we picked up travel guides from AAA and also viewed travel videos on YouTube. Rick Steves has some great videos here https://www.youtube.com/user/RickSteves.
Most airlines allow one checked bag and one carry-on piece of luggage per person, some also allow for n additional personal item as well, i.e. a laptop bag, purse, or camera bag. The maximum allowable weight for checked luggage on an international flight is 23 kg or 50 lbs anything over that and you will either be charged extra or they might not allow the bag on at all. Also keep in mind that souvenirs will add to the weight of the bags on the return flight. You will also want to pack a change of clothes in your carry-on luggage.Why? you might ask, because checked baggage can sometimes get lost in transit, especially if you are switching flights half way through your trip. Also, instead of packing one bag per person consider distributing everyone's clothes equally between all your bags. For example, instead of all my clothes being in one suitcase I placed three complete outfits in each suitcase, My wife and daughter did the same. This was to make sure if a bag got lost, everyone would still have clothes. It also evenly distributed the weight across all three bags. Also remember the 3-1-1 rule: 3.4 ounces (100 ml) bottle or less(by volume)of any liquid placed in a 1 quart (1 liter) sized bag per person. This rule is for carry-on luggage, larger sizes can be carried in checked baggage.
Don't Be Afraid to Try New Things
This should be obvious but you may want to prepare your picky eaters to attempt new and exciting things. this goes for you too, mom and dad. Go with the expectation that you will try at least two new dishes if not more. For example, While in Rome both my wife and I decided that we wanted to try Gelato, honestly we had never had it before, and carbonara. Not only did we try those but we also fell in love with panna cotta, and the lemon ravioli my wife had one night was out of this world.
Dress to Travel
I'm not saying you have to throw on lederhosen like the Von Trapps, but you should be mindful of what to wear. First you need to be conscious of how airport security works. Don't wear anything metal if you can avoid it, gold doesn't set off the metal detectors but steel does, so no watches or bracelets. No belts unless you absolutely need one, you will have to remove it to go through security. You will also have to remove your shoes, at least in the USA, so wear something that can be slipped on and off easily. Also no pants with chains or excess rivets unless you like being patted down.With all that being said I recommend wearing comfortable tennis shoes and loose fitting jeans or khakis with a t-shirt or polo type shirt. Keep in mind that the plane is Air Conditioned and is usually a might chilly so unless it is a short flight I don't recommend shorts. Depending on when your flight is scheduled you may be sleeping in these clothes so again keep them loose and comfortable.
Secure Your Valuables
When ever I travel to a large tourist city, even if it is just a day trip to New York. I always keep my wallet in my front pocket. I've never been pick-pocketed, and I don't plan to be, so I don't make my self a target. Women are not immune either so I recommend either ditching the purse and getting a wallet to put in your front pocket also or if you are using a purse, use one with an adjustable shoulder strap and wear it with the strap crossing your body keeping the purse itself close to the front of your body. Also. as I told my daughter if in a crowd hold onto your purse keeping it against your body, it makes it more difficult to snag and thus reducing your likelihood to be a target. I also recommend that if your hotel room has a safe that you use it. There is no reason to carry all your credit cards and money with you every time you leave the hotel room.
It's vacation after all it should be fun and stress free. Don't try to see and do everything in the country or city you are visiting, just do the things that will create the best memories and remember to plan in some down time to just relax.