I think you and your chickens will be just fine! Most folks here who use leaves and grass clippings make sure there is not pesticide or herbicide on it, so something to be considered. I even asked about "are pine cones ok" a while back and was assured that they were. The more variation in materials the better and leaves are perfect as are the rotten logs (which are like gold for deep litter and I have used them too!). Even shredded paper!
Thanks for the advice. I put everything in and the chicks haven't come out of their coop yet I don't think they know what to make of it.
Myrna