Hi Alexis!
Welcome to the Disney Parks Moms Panel! I'm an only child, and I currently have just one son, so I've been both the single kid and the plus-one parent. Rest assured, there are plenty of attractions that your whole little family can enjoy together!
Walt Disney World Resort was built for families, and most ride vehicles are two rows per car or are bench seating for everyone. In my experience, ride vehicles with just one row and no height requirement usually allow a lap child. And some single row vehicles even fit three adults, like the Haunted Mansion, The Seas with Nemo and Friends, Peter Pan's Flight and more. Ask the Cast Member at the entrance to each attraction if they think your whole family can ride together in one car so you can make your game plan before you get in line.
Buzz Lightyear's Space Ranger Spin can fit two adults and a small child, but families often split up so everyone can have their own space cannon. The ride vehicles are only a few feet away from each other, and even though you won't be in the same space you'll still see all the fun. In fact you might have a better view this way as you can see your child's smiling face mid-ride. I prefer to experience some attractions this way so I can take pictures of my son and husband having a blast, then we switch rider/photographer on the next attraction. However, if both adults wish to ride with the child, some attractions do offer a
Rider Switch option. Adult One can experience the attraction with the child while Adult Two waits behind (and takes this time to shop or get a snack), then Adult Two can ride and with the child while Adult One takes a break. On rides where Rider Switch is not offered then parent two will have to stand in line with the child to experience this attraction together.
I hope this helped and We'll See You Real Soon, Alexis!
~Kristen