Once you and your baby have secured a job, you may be surprised to turn up to set and find one or more similar looking babies also booked for the same job. This is because we know babies are unpredictable. They might have been the happiest little cherub in the world, but on the day of the shoot suffer an awful toothache or be hungry or irritable etc.
Casting directors compensate for this by having at least one back-up baby on set ready to substitute in depending on the results. You and your child will be paid either way for your time on set. However, if your baby is used in the final cut, you will often get an additional usage fee. This is negotiated on your behalf by the agency.