Baby Cart in Peril (1972)

AKA Lone Wolf and Cub: Baby Cart in Peril. Kozure Ōkami: Oya no kokoro ko no kokoro.
"Those eyes."
Ogami Ittō, the disgraced former shōgun's executioner is hired to kill Oyuki, a tattooed female assassin, but whilst traking her down, Ittō's 3-year-old son, Daigoro goes missing.
The forth episode in the Lone Wolf and Cub series, mixes up a number of story lines including Daigoro showing his independence and resourcefulness.

sword of vengeance (1972)

AKA Lone Wolf and Cub: Sword of Vengeance. Kozure Ōkami: Kowokashi udekashi tsukamatsuru.
"I will make sure the shōgun settles this matter."
Set in Japan during an unspecified year of the Edo period, Tomisaburo Wakayama (Ogami Ittō), is a disgraced former Kogi Kaishakunin (executioner) to the shōgun, wandering the countryside, with his 3-year-old son Daigoro inside a baby cart.
The start of the Lone Wolf and Cub series, starts Itto's bloodbath journey across the countryside and delves into why he is an assassin with child.