Katydids are closely related to grasshoppers and crickets (they are all classified as Orthoptera), and the easiest way to tell katydids, at any age, from grasshoppers is the length of their antennae.
This little one (8-10mm long) seems to have overdone it somewhat but is perfectly normal – see, for instance, a differently coloured one I photographed in April. When it grows up it will look something like this or this, but it is often impossible to know the exact identity of a juvenile insect.
