Not as simple as that. The property in the hands of children is ancestral if property acquired by partition is property belonging to joint family. Let's proceed like this :-
On partition he alongwith children becomes entitled to 1/5th each. (Note : No share to wife in lifetime)
On his death his share i.e 1/5th devolves on children and wife in equal measures - that is 1/25th
Hence in the ultimate analysis widow - holds 1/25th - children hold 1/5th + 1/25th = 6/25th each.
Good luck for the moot