You have to accept it.  Cats are fowlers.  Cats and fowl (birds of any
kind) are arch enemies and the cat will always go after the fowl.  You
can't expect the cat to just sneak around in the bushes or the flower
beds in order to catch AND KILL the fowl, like chickens or sparrows or
something like that.  Its normal for the the cat to do his business
right on the lawn and snag the bird right in front of the children
which does cause a bit of chaos.  It might be best if you didnt keep
chickens AND a cat in a small garden if you do not want your child
exposed to this kind of mayhem.   Dont worry about your child.  He
will be potty trained before you know it and will have no memories of
his tiger cat doing  business right in front of his eyes snogging up
chickens and sparrows and wrens etc.