J.P.
My son was like that, from the day he was born. ONLY mommy would do. If he didn't have me he screamed and screamed. Even dad could not do anything for him. When he was 25 months old, we had another baby. This is what finally got him over the "only mommy" phase. When his sister was born, and needed my attention, my son realized that he was going to have to let daddy help him too. Now, he LOVES his dad, and if he has a choice, daddy is always his first pick.