Yes babies are cute - I have one so I know. They coo and giggle and men and women have been known to go gaga over them. But when it comes to your wedding you have to think about the bigger picture.
A baby who can't walk or even one who just started, let's just say anyone under 5, may need to be accompanied down the aisle by a parent or close relative. A child that young may easily get stage fright and freeze halfway down the aisle or worse start crying and screaming.
To prevent either from happening either have an adult walk or carry the little one down the aisle. If he or she is big enough to walk on his or her own then have a friendly face drop him/her off at the start of the aisle and another friendly face near the altar. This way he or she has someone to walk to.
The truth is it won't be the end of the world if your little flower girl or ring bearer doesn't make it down the aisle in the end. Just make sure that there is a friendly face who can either help him or her on their way or scoop him or her up in case of a baby meltdown.