Ding Shuwen, 26; Feng Jiayuan, 11; and Liu Hao, 9, are among dozens of Chinese citizens who say they've been hurt in recent years by the weapons, abandoned inChina by Japanese forces who invaded and then left.
The three are in Tokyo this week to meet with government officials to ask for support - without going to court, because they want a long-term assistance fund to be set up instead of one-time compensation.
They have complained of painful blisters on their legs and hands, weakened vision, coughs and chronic fatigue.
Ding and Feng are among 43 people injured in 2003 when construction workers broke a buried barrel of abandoned poison gas in northeastern China's Qiqihar city. The incident killed one person, the AP reports.
Liu's leg and hands were hurt in 2004 when the child touched a poison gas shell in a riverbank in another northeastern city, Dunhua.
A 1997 international convention requires Japan to remove the weapons within 10 years, but Japan has asked for a five-year extension. The status of the request was not immediately clear.
Japan has so far removed 37,000 chemical weapons, though at least 700,000 are believed to remain.
Tokyo has agreed to pay 300 million yen (US$2.7 million; Ђ2.2 million) in compensation to the 44 Qiqihar incident victims.
However, Ding, Feng and Liu, along with their relatives and attorneys, arrived in Tokyo Saturday on a nine-day visit, were to ask the Japanese government to set up a fund to provide them with long-term support.