As a parent, you need a certain amount of patience to use a catheter on a child. (Especially when that child is 2-4 years old with a strong will of its own.) It can be comforting to know that CIC after all is one of the most gentle ways to empty the bladder of a child that cannot urinate in a natural way.
Emptying your bladder is a private matter
It's important that your child learns that emptying his/her bladder is a private matter, which should be done in the toilet. You should therefore start catheterising your child at the toilet as soon as possible. If your child wants to participate, let it for example help to fill the catheter package with water or perhaps carefully pull the catheter out after emptying his/her bladder. You can also acquire a special doll on which your child can practice inserting a catheter.
Consult your doctor or continence nurse for more suggestions.