In a pram they would have to be lying flat unti old enough to raise up a little. Some prams have a bassinette for this reason. In a capsule or in a car seat - it is a gentle incline so I wouldnt think so. Inever used a capsule and had a nicely padded car seat that supported her though. Some prams also come with a u-shaped pillowy thing to support them!
HtH!