No, because three weeks is too young for cereal.
It is believed that adding rice cereal to the bedtime feeding
makes a baby feel fuller for a longer time. So, a baby sleeps better at night. It is ok to add some cereal this way, if the baby is over 4 months old and still not sleeping 6-7 hours at night. Parents should be sure to put the baby down at bedtime and let him fall asleep on his own.