One thing I want to emphasize as we work on some fun science experiments with little ones is the skill of communication. My high school students were probably (very) sick of my saying this, but the most repeated line in my classroom was, "Support your answer with evidence". In order to do that, the experiment had to be well documented including both quantitative (numeric) and qualitative (word) observations, procedural information, drawings, questions and any other findings they had made.
At the young ages of my girls, I'm obviously not looking for the same level of documentation, but I figure it is good practice to get them started drawing pictures of what we are doing, some simple bar graphs (I'm envisioning some fun M&M counting experiments after Halloween) and, for my older one, a chance to practice writing. It also is an easy thing for the girls to show their daddy when he get's home, "Look what we did, Daddy!".
To accomplish this, I looked around the house and gathered some materials I already had on hand (I didn't really want to go out and buy stuff), including: 6" x 9" foam sheets, foam letter stickers, and a 1/2" spiral binding for my Zutter Bind-It-All. I also found some penmanship font on one of the free font websites and made a simple lab sheet that I printed front and back, about 20 for each book. I used the foam because I was hoping for something a bit water-resistant, but if you want to make a journal then you could easily use card stock as the cover.
Here are some pics of the finished books. I've already made some improvements of the lab sheet (penmanship font at top for title, options of both 3 and 4 lines under the drawing/graph area), but for now these will do for the girls.
UPDATE 11/30/11: I think I've figured out a way to provide a direct link through Google Docs. Don't worry: you don't need to have an account and you don't need to sign in to any file sharing service. This link should take you right to the pdf. There are two pages - one with 3 lines for writing and one with 4, depending on how much space your child needs. Let me know if you have any problems and, if you use it, and you have any suggestions for improvement! Thanks!