The answers given by his children were:
Darius: "Index finger."
Brenda: "Middle finger."
Alfred: "Ring finger."
Eric: "Little finger."
Details and assumptions:
Mr Tan has five fingers on a hand like anyone else haha.
Mr Tan counts exactly one number for each finger.
Whenever Mr Tan reaches his thumb or little finger, he counts only one number there, after which he reverses direction.
Yes, one of the five siblings MUST be correct. But which one???