Hi Debbie,
Thanks for visiting the Disney Parks Moms Panel with your question. You are considering two great restaurants! I have been to both
Le Cellier Steakhouse and
Yachtsman Steakhouse and have had good meals at both. I think that either one that you choose, you are going to have a delicious meal.
If I was going to choose one of these restaurants to visit with a five-year-old, I think that I would choose Le Cellier Steakhouse. It seems a little less formal to me than Yachtsman Steakhouse, and I do enjoy Le Cellier Steakhouse a bit more than Yachtsman Steakhouse. A child would be welcome at either, of course. Another consideration that you need to make is that Le Cellier Steakhouse is in a theme park (Epcot) whereas Yachtsman Steakhouse is at a resort (Disney's Yacht Club Resort). So you will need theme park admission if you choose Le Cellier Steakhouse.
The unofficial website wdwinfo.com has menus for both of these restaurants. Go to wdwinfo.com, and under "Dining," click "Menus" and then search for each restaurant. These will give you a good idea of currently offered adult and children's menus, so you can take a look at which restaurant better suits your family's needs.
I hope that this information helps, Debbie! Please do not hesitate to ask if you have any further questions, and enjoy the delicious food when you are at Walt Disney World!