How to Smile is another great free site for STEM focused hands-on-activities. From their site:
Howtosmile.org is collecting the best informal science and math
education activities on the web, and creating tools to help those who
teach school-aged kids in non-classroom settings.
This site is free to register and free to contribute. They have an in depth advanced search function with age, subject, material costs and even a special search by chemical. I did a quick search for Acetic acid (vinegar) and it came up with several fun experiments using this household item.
I think this resource along with Teachers Domain will be a wonderful supplement to Building Foundations of Scientific Understanding, since Blue loves hands on experiments.