I know from helping with the "junior golf league" at my local course that any kid over 7 is likely to hit their driver/fairway wood (often one and the same in kids' sets) around 150 yards or more if they're older. By age 12 there's usually 2-3 of the boys who just try to cream it and will occasionally knock one out there to 250, but they're usually inaccurate. However, from ages 3-5 you'll see big swings and big misses mostly. When they do make solid contact it will go a little ways, but not too far.
One other thing to note for kids in the 7-10 year old range: They hit a 7-iron and a fairway wood pretty close to the same distance up to a point. A lot of the kids will hit their fairway woods around 150 and their 7-iron 125. My guess it has everything to do with quality of contact, just since a 7-iron is a much more forgiving club especially when hit from the ground. As far as wedges goes it can depend greatly upon technique. Some kids think that they're supposed to deloft their wedges in the swing, since people told them to do that for chips, and hit it as far as a short iron and other can scoop it and end up with it going nowhere.
Here's what I would call a general "yardage chart" based on age groups.
3-5 years - ~50-100 with fairway wood, maybe 30 with iron, and around 15 for a wedge. Highly inconsistent contact, often only going 10 yards or less with any club
6-8 years - ~125-175 with fairway wood, probably about 75-100 with an iron, and around 50-75 for a wedge. Contact more consistent and kids getting bigger
9-10 years - ~150-200 with fairway wood, somewhere in the range of 100-125 for an iron, and likely 75-100 for a wedge. Some kids in this age group will excel and be able to beat you with a stellar short game to compensate for lost distance. You also may get a couple kids who play terribly because the only thing they care about is how far they can hit it.