No they'll be fine, just don't let them catnip and drive!
Cats react differently to catnip. Some act like they're in heat, others don't react at all, I had one who looked stoned after rubbing on and eating fresh catnip.
It isn't toxic. Just watch how your cats respond to it, if they do get sort of stoned, try to keep them in till it wears off. I wouldn't have trusted Polly to negotiate the top of the garden fence safely.
Let your cats loose on the catnip, it won't harm them. I hope you have it in pots and not growing in a flower bed because it will take over; it grows like mint, easily and rapidly.
