We belonged to the Gate City Striders when I lived in Nashua. We kept our membership even after we moved to Concord so we could get their newsletter, follow club members times and also for discounts to Runner's Alley. We let our membership run out about 2 years ago. I have to say that for NH- it is the best running club up here. We had only positive experiences with them. When I lived in NJ I belonged to 2 different running clubs which were great. It is harder to find clubs up here-I suppose because of less population and the weather.
I don't know an awful lot about the youth program but I found this link-maybe you already have it since you mentioned the Striders. This is the only youth running "club" I know of in your area for kids. I am unaware of any stand alone youth running programs in your area. I have a runner friend who still lives in Nashua-I will send her an E-mail and see what else I can find.
Gate city youth
http://www.gatecity.org/AA/index.shtml (broken link)
I also know GC Striders run youth clinics and other events throughout the year. Do you get the Telegraph? I know there used to be a column on I think Sundays about the running scene and the Striders. Of course this was some time ago.
I will let you know what my friend says. Sorry I don't have more info.
Nicolem