I'm attaching a link for a PDF which I found online specifically for children with autism, but I don't think it matters it'd just a great resource for any child. I'm pretty sure the link is okay to be published here. There is a similar one for professionals as well. I just googled " autism relaxation blood test" to find it again.

It's useful for lots of different reasons children might be anxious, but had been specifically written for taking blood

http://sutter.networkofcare.org/libr...raw-parent.pdf