New grandson: photo 4 (18 days old)

Took some sunny blue sky shots this morning but new first grandchild won the blip contest yet again! (See also Jan 5, Jan 8, Jan 14).

Today he's being held by great granny (my mum) who came up from Kent to visit. Other visitors included 2nd/3rd cousins. I never can work out cousin relationships. If two children's grandmothers are sisters what relationship do the two children have?