The ERGOBaby Heart-to-Heart Infant Insert supports the safety of baby's head and neck during this critical stage of development. The Heart-to-Heart Infant Insert from ERGObaby promotes healthy maturation of the spine by supporting the pelvis, hip joint and leg position. 100% cotton batting. For Babies up to 5 months old. Compatible with All ERGObaby Carriers. Please note: If your baby is less than four months old, you will need an ERGObaby Infant Insert in order to safely carry your baby in the ERGObaby Carrier.