If something is going on, Max wants in on it.
And if at all possible, Elliot wants to help him. I'm guessing that is because she still sings the "me too" refrain to her big sister. She knows where he's coming from.
So when the ktichen table chemistry set came out (a few beakers, some baking soda, and Elle's choice of condiments), they both insisted that Max be included.
The result was a duo of experimenters. A bit messy maybe, but a great way to spend the morning.