Hi, Thank you for the query. I hope there is no reason to worry. If these spots were noticed after birth and look like flat bruises with a bluish hue and are located at the back and thighs...they are probably Mongolian spots..these are usually discolouration of skin from birth bearing no clinical significance. Spontaneous bruising occurs in haematological conditions. But those lesions will disappear to reappear again specially at the sites of trauma or injury. In that case the child may have bleeding from elsewhere too.In that case consult a haematologist. Until then there is no reason to worry.Enjoy parenthood.