Set your radio to a music station and have your child turn it off and on. Every time they turn it on, start to danc””or move aroun””and say “on” When they turn it off, stop moving and say “off” Soon they will probably say “of” and “o” with you.
See what your child is learning
Learning new words and concepts (like “of” and “o”) is much easier at this age if your child can make something happen (like turning music off and on.) This helps add context to what these new words mean.