During the ceremony that lasted more than two hours, Francis baptised 18 girls and 16 boys, including two pairs of twins.
“If they start performing a concert (by crying), or if they are uncomfortable or too warm or don’t feel at ease or are hungry … breastfeed them, don’t be afraid, feed them, because this too is the language of love,” he said in a short improvised homily.
Women still face harassment for breastfeeding in public in some countries even though attitudes are changing.
The pope has made similar comments in past ceremonies. Television pictures showed at least one mother bottle-feeding her child.
The papal baptism is a yearly event restricted to children of employees of the Vatican or the diocese of Rome. Francis is also bishop of the Italian capital.
The most famous frescoes in the Sistine Chapel – the ceiling scenes and the Last Judgement wall – were painted by Michelangelo.