Now you are talking about something I have experience with!
We also have the child's first Holy Confession at age 7. The age is NOT set in stone. If the parents feel their child is not mature enough...then we wait. I've had them as old as 12. There's no real age limit, but, usually not younger than 7...because they won't understand right from wrong, yet.
We usually have their First Confession on Palm Sunday. The girls usually dress in white...but, not over the top...no veils, tiaras, etc. The boys also dress in suits. I have them hold the candles during the reading of the Gospel and the boys during the Great Entrance....it makes them feel extra special.
I also get them pretty white corsages/boutonnieres.
After Divine Liturgy the priest hands them the certificates I print off, which he has signed and an icon of Christ the Good Shepherd.
Three weeks prior to this, we hold classes after Divine Liturgy. I provide them the booklets I made which I hope the parents review with them, as 3 hours is hardly enough time. We go over the importance of Confession, the Creed, the Lord's Prayer, etc.
Over the years I've figured out how to make the biggest impact on them concerning sins and Confession.
In class I hand them tiny slivers of paper and have them sit and think of any sins they have committed and write them down. I promise that nobody is going to see them, and they need to be honest. Once the kids are done (and some have asked for more paper)....I have them put their little sins on a pretty little paper plate I gave them....then we go to church.
We've already walked through the "steps" in class.....but, now I stand in for the priest...and they come up for confession. I tell them to place their plate next to the Bible, so that their hands are free to place on the Bible, etc. They bend their heads so they can hear what Father will be telling them (but, they just pretend with me...and don't tell me anything)...most end up shutting their eyes. I put my hand on their head and tell them Father will do likewise with his stole and not to get scared...at which point I grab the plate and sweep the little papers off into a bag I have on the side. When the child finishes and leaves, I make sure to call them to remind them to take their plate and boy are they surprised to find their "sins" are gone....and their plate is empty and clean.
Works like a charm.