When I make Beef Congee for my son, I cook it the same way as making adult congee but without putting in any salt. When it is done, I puree the cooked beef slices with my hand blender into minced beef and then add back into the congee to serve to him.
Be sure to feed your baby the beef and not just plain congee with beef taste, or he/she is not getting the nutrients from this meal. You may also add in vegetables when the congee is almost done (do not over cook vegetables or else you will loose the valuable nutrients) to add extra fibre and vitamins/minerals to the congee. :-P