One of the greatest books I've bought for my kids is
Instead of having to journal or write or verbalize prayers that may be difficult at a young age, they can simply do what they already know to do -- color or draw.
If you find your kids turning flips during prayer time or slapping each other or laughing or eating or walking out of the room to get a toy, or I could go on and on (not from experience of course -- feel free to share your own story in the comments), you may want to invest in this book. Summer is a great time to get started.
Here is an example of one of Sarah's colorful prayers: