Ohhhhh... Don't you have client consultation cards then. I know my insurance company requires a signature, and I haven't come across many that dont.
For instance... What would you do if something went wrong, i.e. a reaction to your treatment and the parent then claimed against you/ your insurance, then it would be the parents word against yours over whether they allowed you to carry out the treatment.
No signature = No proof!!
Ekkkkk! As per my quotes I hope this is considered as constructive. All I have provided is advice here!