Dear Laura,
Thanks so much for reaching out to us here at the Disney Parks Moms Panel with your question about booking next year's vacation!
At this time via the website, you may only book
Walt Disney World Resort vacations with a check-in date of December 31, 2017, or earlier. If you would like to book a "room only" trip for April of 2018, you can call 1(407)W-DISNEY up to 499 days before your check-in date, and you can book your room reservation.
If you are planning on booking a vacation package, those dates have historically been released in late spring or early summer, so keep an eye out for that!
Hope that helps you to plan your magical vacation!
- Jan K.