Hi Janet, Thanks for visiting the Moms Panel!
We have a family of 7 (2 adults, 5 kids) and I have a few suggestions for you. First, your most economical lodging solution will be to reserve two connecting standard-view rooms at a Disney Value Resort. We have done this, and found the two bathrooms to come in handy. The Value Resorts are colorful and fun, and I am sure that the youngest 3 children in particular will enjoy them. This is a link to the Value Resorts:
HERE.
When traveling with that many people, we generally just purchase the Base Tickets. This allows one Park per day. We've often found it to be a hassle when trying to switch Parks with little kids. Therefore, once we get somewhere, we stay put for the day. The wonderful thing is that there is SO much to see and do at each Park, you can easily spend a full day (and more) soaking in all of the magic. The Base tickets are less expensive than the Park Hoppers, which is a bonus.
I also recommend that you purchase Disney's Basic Dining Plan. Your infant will be free, and the 5 and 9 year old children will be able to eat one Table Service, one Counter Service and one snack per day for less than $12.00 each! We add the Dining Plan on every trip and feel that it saves our family a considerable amount of money.
Hope this helps and please let me know if you need further assistance.
Have a magical vacation!
Kaylene