Here are PANORAMIC X-rays at different age groups.

This shows the x-ray of a 4 year old. The adult teeth are seen just below the gumline still buried in the bone. The "6-year molars" are just starting to develop roots (shown on both sides in the back.) There is also a mix of adult teeth and baby teeth in the middle.

This shows the x-ray of a 9 and a half year old. The adult teeth are starting to align themselves and the second molars are being well-developed. The
baby teeth are mostly gone, with the exception of one baby tooth still in the upper right of the film just before the molars.

This shows the x-ray of a 16 year old. The adult teeth are basically in alignment and the wisdom teeth are starting to come down and develop on the upper.