Children in weddings are...so cute especially if you are a guest. For the bride or mother of the bride...not so much. Even if they are your own. Why? because they are the one aspect TOTALY out of your control. They may or may NOT walk down the aisle on que. They probably at some point will melt down and there is a pretty darn good chance that at some point they will spill something. Hopefully it won't be before the ceremony, on you or on themselves but you can count on the fact that your little flower girl or ring bearer will step out of line at least once during the day. If that's a problem for you then you may want to reconsider their involvement.
Kids are naturally unpredictable. They say crazy things in loud voices at inopportune times. They like messy things and are naturally clumsy. It's all part of the growing up process. You can't blame them...it's just who they are and how mother nature made them. They are eager to explore and experince the world and have a really hard time with those impluses that make them guzzle (and dribble) the grape drink or roll down the grassy knoll just before they sprinkle flowers or carry the ring pillow down the aisle.
So all I am saying is, you've seen great photos, really CUTE photos of kids in weddings and no doubt your photographer can capture some great shots of your flower girl & ring bearer but you need to know the whole truth and decide if this is really what you want. Because if it's not, it's better to know now or be prepared!
If you do decide to have little kids participate in your wedding there are many things you can do to help make everything go smoothly. First feed them! Kids nibble. They don't eat big meals. And depending on what was going on at their mothers house you have no idea their state when they arrive so bring a basket filled with snacks and water bottles for your little people.(Warning! Avoid messy snacks!) and this is the one time where over packing might be ok. You may also want to have a few little toys or surprises to keep them occupied while they wait. A bored kid is a miserable kid and if they are unhappy chances are you'll know it! Next have a contingency plan! They could get really freaked out when everyone turns to look at them when it's their turn to go down the aisle. Have someone they trust to help them out or have a plan in case they absolutely refuse.
Finally be patient and understand that stuff happens and sometimes it's the stuff that makes the cutest pictures and the best memories so don't freak out!