I don't know of any reason a non-profit couldn't save for the future (as far as jeopardizing it's status). They aren't required to spend all incoming funds. By policy, most of the groups seem to want to spend the funds the same year so the children raising the money benefit. Common execptions include retaining some start up money for the following year and if the group is saving over multiple years for a large item - like maybe a playground. If that's the case, it might make sense to save it in a secure, interest bearing instrument like a CD.
My question would be "what is the reason for saving a large amount?" (And, by the way, what's "large".) If it's a purpose with which the membership agrees, that should be fine. If not, this needs to be resolved.