Speed warning sign not visible or detectable ( improper size)

There is tiny 30mph sign at the top of the Dungells lane as you enter a residential road that has a school. It has been raised to Newlands school as a risk, as many drivers don't see it, speed from Vigo Lane and onto Dungells bends as they enter key child crossing zones and also unpaved roads. This sign needs to be made bigger (its tiny) and road markings to indicate as its no longer adequate and car road sign recognition does not pick it up.