I read this last week in the Michelin guide to Provence:
… St-Pantaleon’s Romanesque church is built out of the living rock and consists of three naves; the central part dates back to the 5C.
Surrounding the church is a rock necropolis, most of the tombs of which are child-size. This necropolis was most likely a sanctuary of grace; there are other examples like it in Provence. Children who died before they were baptized were brought here by their parents, they revived–according to the beliefs of the period–for the duration of a mass during which they were baptized, they then died again and were buried here.
Intrigued, I visited the site twice, since it was only 4km from where I was staying. The church was small, and the first time I went, in the evening, I didn’t even see the necropolis, but only the small cemetery with large, newer tombs.
The second time, in the morning, I found the necropolis to the side and back of the building. It is as Michelin described: graves carved right into the rock, a few adult-sized, but most the size of a baby.