This is a killeen, the Irish term for an informal burial place reserved for unbaptised infants, children who died before they could receive the sacrament and were therefore excluded from consecrated ground under Catholic doctrine. The practice was widespread across Ireland for centuries, and killens are often found in marginal or liminal spots, old ringfort interiors, cliff edges, and island shores, places that sat outside the ordinary geography of parish life.

The enclosure at Rossmore is defined by a drystone-faced wall, the kind of unmortared stonework built entirely from local material without the use of lime or cement, though it is now poorly preserved and heavily overgrown. What survives is most legible on the north-west side, where the wall still stands roughly thirty centimetres high and measures about one and a half metres across. Inside, loose stone is scattered across the ground, and in the south-east quadrant a series of small upright grave-markers are arranged in north-south rows, averaging about half a metre in height. These modest, uncarved stones are the only formal acknowledgement that people lie here. Local tradition, recorded by Ó Cíobháín in 1984, holds that adults were buried at the site as well, alongside the children for whom it was originally intended, which was not unusual where a killeen became the only available option for families at the margins of parish structures.