Disney lifeguards will not allow these anymore years ago you sometimes could get by with one depending on the lifeguard on duty....now it's a definite no( in our experience)....obstructs their view. With DD1.... I just held her at 6 months in the pool. You all will still have a great time!
Edited to add....you most likely could bring it for the quiet pool at your resort....no lifeguards there,!!