Having some of the smaller members of your family involved in your ceremony can be a very sweet and personal touch. But try not to stress about them performing perfectly- there's very little they can do that would actually ruin your day. To keep things in perspective: 

- allow them to practise, but don't stress out about timings

- try to encourage the adults not to make too big a deal of it (this way they wont know there's anything to be nervous of).

-having a special job, like sprinkling flowers, can be a good thing to focus on and feel important.

-go with the flow! If a ring bearer ducks out at the last minute it wont matter. 

One of the cutest flower girls we saw this year didn't want to let go of her Daddy's hand, so he walked down the aisle with her. It wasn't planned, but it was very sweet.