All passengers need tickets for international travel. If passenger is under two years of age, 10% of the adult fare is charged if they are going to sit on your lap. If the child wants a seat or is between 2 and 12, discounts range from 25% to 50% off depending upon the routing and airline.

Since all passengers need a physical ticket, there is no way you will be able to bluff your way through check in w/o having to pay.