A little boy went missing from a Sydney daycare centre for several hours after a grandfather accidentally took the wrong child home.

The mix-up at First Steps Learning Academy in Bangor, in the city's south, was only discovered when the boy's mother arrived to pick him up.

However, to the woman's horror, she realised her son was missing.

Panicked staff reviewed CCTV footage, which showed the grandfather being handed the woman's child, instead of his grandson, and leaving the daycare.

His emotional wife explained it had been nap time when he arrived to pick up their grandchild and the room had been darkened.