Step 1: The task is to spot the one constitutional provision that does not deal with the welfare of children.
Step 2: Article 21-A (right to education for 6 to 14 years), Article 24 (ban on child labour in hazardous jobs) and Article 23 (protection from trafficking and bonded labour) all extend clear protection to children.
Step 3: Article 42 instead asks the State to secure just and humane working conditions and maternity relief, so its focus is on labourers and mothers rather than on the child.
Step 4: Since the other three articles centre on children and only Article 42 does not, it is the odd one out.
\[\boxed{\text{Article 42}}\]