This is really not a cut and dry case to give guidance on.  You have rights as do your tenants below you. And kids make noise.  That is the bottom line.  If she is a legal tenant - meaning that you rented and the landlord knew she lived with you - then you need to do some stuff to lower the noise below.  This could be as simple as putting down some rugs or limiting your grandchild to a certain space - not confining her but limiting her - at certain times.  Like maybe to the living room in the early mornings so that the playing does not disturb the tenant below while they sleep, etc. You need to take "mitigating" measures. As long as you are cognizant and take steps to reduce the noise and disturbance then you should be fine.