a three month old fits nicely into a front pack carrier. another option that grandmother is bound to have, is a yard or two of fabric and carry the infant on her hip. You place the child in the middle of the fabric, situate the fabric on hip, back where ever you want and wrap and tie the fabric around your shoulders. i and many other hippie moms and Indigenous woman all over the world have hauled infants around like that. they sleep nicely, all safe and secure.