i am going to book flight to hawaii with delta. On their site, it said that if i am going to hold my baby in my lap, no ticket needed. Is this true? How do I let delta know about him coming with us ? Finding this board, i find out that people said that they had to pay a lap fee. What's the correct answer? Thank you

I need to book flight as soon as possible and and I buy two adult tickets now and call delta to add the baby on as a free lap baby?