This question already has an answer here:
Wouldn't the British Parliament wonder where the Muggle-borns students who were supposed to attend their school have gone to?
Or at least, question their parents about their children's whereabouts? And when the child returns home to the Muggle world in the summer, question the children themselves?
Wouldn't they or shouldn't they have been able to intercept at least one letter of invitation and acceptance to a Wizarding School like Hogwarts from like, an owl?
Or better yet, why didn't this guard report to the public that Harry and Ron attempted to go through a platform before flying the Ford Anglia and were witnessed by no less than seven muggles (Chamber of Secrets), and possibly questioned both of them at the end of the second year?
Or even better, question everybody else that seems to enter and/or leave Platform 9 3/4 for whatever levels of intents and purposes?