If you're staying at one of the three resorts you can have an "in room celebration".....they show you what those are on the disneyland.com website. Just keep in mind, that they are unable to change anything that's offered (so if you wanted a different gift basket, etc)....they won't be able to do that. You can have balloons left in your room. $1/piece. You also could order a basket thru them as well. The baskets can be delivered to some of the Good Neighbor motels, but it will be left at the front desk for you to pick up.
Character meals are always a fun way to spend a birthday......no matter the age!!! I'd much rather spend a little more on one of those than do the Pat-E-Cake party again. My 2 young kids hated it. My 3 yr old turned her eyebrow red from the dye in the frosting.....the cake was dry......you can do a quick pic with Mickey & Minnie......but you can get more interaction at a meal....plus an autograph if you want them. (you can't get an autograph at the party)
You could also chose a nice dinner at the Blue Bayou.
Make sure they wear a birthday button, they'll get lots of birthday greetings!!
You could ask to ride in the Wheelhouse of the Mark Twain, or ride with the pilot on the Monorail.
Most of the sit down restaurants will bring out a small dessert for the birthday person or you could arrange with Disney Dining to have a cake done for the group.
