a sickly child might well have been baptised on same day (and illegitimate children seemed to be more sickly than others in terms of early deaths) - usual give-away in Parish reg is 'private baptism' and/or two appearances in the IGI (the second being the 'received into the congregation) - I noticed in the parishes I've looked at that the official transcription generally choose the latter over the former if they both occured on the same line.