Well if you want to assume that they do have the capability to have faith in Jesus Christ then you can go ahead and do so. I would be interested in your thoughts on that though.
Perhaps I can answer your question directly. I am the father of 4 boys so I do know what babies are like. I can't see them haveing faith in Jesus Christ because they don't show they have faith in anything. When they get hungry they don't show faith that they are going to be feed, they just respond to their hunger and demand to to be feed. Likewise with a number of other things.
Infants have to go through a period of learning before they can do anything on their own much less wonder about who created the universe. Infants spend their time learning about the universe around them and it's not until much later when they can even have thoughts about who created it all.
Trust me, LOL, infants don't have faith in anything. They only know how to respond when their body needs or wants something. Their minds develop fast however, some faster than others.
yah know, I know a guy who told me he was 4 when he gave his life to Jesus Christ and was baptised. He's a minister today in his 30s.