Hilchos Pesach – 9 / searching for chametz

1. Holes or protrusions in a wall that are above the height of a person and are out of reach, or that are very low, such that they are not commonly used – do not need inspection. But if the person knows that he did use those places for chametz, even once during the year, they do need inspection (Shulchan AruchandMishnah Berurah433).

2. In a home in which there are young children, even very low places must be inspected, because it is likely that the children placed chametz there (ibid.).