No, only criminals would be criminalised. These speed changes would be sign posted. A lack of traffic calming doesn’t justify speeding.
These changes will bring down the average speed of cars. This difference has a big impact on reducing the likelihood a child dies from an impact. It also reduces the likelihood of an impact occuring.
Your argument of the change won’t reap the most benefit so we might as well do nothing is shortsighted. I could be your not shortsighted, rather you don’t care and do want any change that might inconvenience cars.