Doctors recommend that your baby be at least 6-8 weeks old before riding in a stroller outdoors in a seated position, as they cannot properly support their head or regulate their own body temperature. Babies under 3 months need to lie flat for correct spinal alignment, freedom of movement, and may turn their heads to spit up.
All of these strollers have a carrycot adaptor so that the stroller can be used for infants under 6 months of age. Some come included, others you'll need to add on.
It's not recommended that you take the stroller on rough or bumpy roads until they are over 6 Months old, but if you live in a rural area and don't have another option, you'll need to use an infant car seat and find a stroller that has a car seat adapter that allows you to clip the car seat into the stroller.
Please consult with your doctor about the proper stroller recommendation for your child.