I would be assured that if the school is offering them they are legit. Schools frequently offer this sort of thing as a PTA fund raiser which would indicate that other schools have used them successfully. Just call the school and ask about them.
I looked at the web site. This sounds like the company is using the ID package for children as a way to sell the school on their expensive visitor screening package. The school or PTA doesn't get a portion of the proceeds. They do get certain security products.
I'd say this is not a scam but it is a marketing gimmick. I would call and ask the school for more information about how this benefits the school.
My daughter bought an ID package at a Babies R Us store. The cost was minimal. I don't remember exactly but less than $20. Positive Proof's web site doesn't list prices and actually doesn't give much information about the individual packages that they're selling to families. Whether or not I purchased any of their products would depend on the cost. If it's more than $20 I would wait and look for other companies providing the same services and compare prices.
The package my daughter bought was fingerprinting and picture ID. They gave her the actual finger print card which is all that the police would need. No need for digital (can't remember their terminology) And as to the ID card, all the police need is a current picture of your child.
I'm a retired police officer and would think twice about spending much money on an ID package. The likelihood of ever needing finger prints is next to nothing. While your child is in school they have a picture ID. At least in Portland the school district issues picture ID.
I suggest that you could probably purchase a smart phone and a home DNA kit on your own for less. Why would you need DNA, actually? If it was needed the police can obtain it from items you have at home. I suggest that companies such as this pray on the fears of parents.
Just things to think about.