If your camp has been set up to allow you to set limits on specific groups - eg if you have 10 spaces for children Born 2012-2013 and 10 spaces for children born 2014-2015 and you need to check how many sales you have in each group.
Firstly on the Camps & Events Dashboard select Events and chose your camp from the list.
Click Manage
Then choose Edit
Scroll to Optional Extras section
Select Edit
You can now see the limits (in this case total of 10 spaces) and in the shaded box you can see how many are still available.
Eg in Born 2012-2013 there are 9 spaces left of a total of 10 available spaces and in Born 2014-2015 there are 8 spaces still available of a total of 10 available spaces.