Hi Kirstenh!
How exciting to be going on your first Walt Disney World vacation! Your family sounds like mine. I have five children, but three of them are the same ages as your children. Don't worry; you will have plenty to ride on with the whole family. In fact, this is one of the main reasons why the Walt Disney World resort is our family's favorite destination--lots of together time!
Your 1-year-old will be able to ride on any attraction without a height requirement. I remember the look on my babies' faces as they soared high in the sky on Dumbo the Flying Elephant. The same thing applies to your 3-year-old. Depending on your 5-year-old's height, he/she may be on the border of meeting height requirements for attractions such as Splash Mountain which requires Guests to be 40 inches or taller.
If you or your husband are thrill seekers and want to scream on Space Mountain, then please take advantage of the
Rider Switch program. I don't discourage you from bringing grandma along; it's always nice to have an extra helping hand. We often bring my mother along to have a date night or two. But rest assured, it's not a necessity. Your family will have a fabulous vacation full of magical memories!
If you have any other questions, please ask away! I love answering all your Disney vacation planning questions!
Wishing you pixie-dusted dreams,
Tania