Labour attacked Liberal Democrat support for lowering the drinking age to 16 as party leader Charles Kennedy visited his main Welsh target seat.
Mr Kennedy reading to children at St Monica's primary school, Cardiff
Labour said cutting the age was "wrongheaded and dangerous".
Lib Dems said while mature drink attitudes were needed, 16-year-olds needed to be treated as adults.
Conservatives backed an increase in overseas aid, and Plaid Cymru urged shoppers and governments to "buy local, Welsh, organic and British".
Both Lib Dem and Labour supporters with placards and posters were waiting when Mr Kennedy arrived at a primary school in Cardiff Central, where his party hopes to overturn Labour's 659 majority.
Labour said more than half of all violent crime was drink-related, and lowering the age limit would lead to police having to look for 14-15-year-olds in pubs and clubs.
From Monday, underage drinkers can be fined under new legislation. Labour also plans to force pubs and clubs to pay towards the cost of drink-related trouble, and give police the power to shut down places for 24 hours if they sell to underage drinkers.
The Lib Dems said they wanted to "extend full social and political rights to 16-year-olds."
Shoppers in Cardiff being urged to go to the polling booths on 5 May
"At 16 you can get married, pay taxes, and join the army; if you're mature enough to make those decisions, why should you be treated as a child in other respects?" said the party.
Asked if the Conservatives were "scaremongering" over immigration and asylum, the Lib Dem leader said it was "perfectly sensible" to have a debate, and his party wanted a "properly managed, controlled" system.
Welsh Tories gave their support to Oxfam's World Poverty Day on Sunday, and said a Conservative government would increase aid "as part of wide-ranging proposals to tackle poverty around the world".
Tories would increase spending by the Department for International Development by £800m over three years to £5.3bn, and concentrate more on areas such as public health.
Nick Bourne, leader of the Conservatives in the Welsh assembly, said: "We must do everything we can in the developed world to combat poverty in the poorer nations.
"As a country we have a responsibility to help all those around the world who are less fortunate than ourselves."
Plaid Cymru claimed the election so far had ignored the importance of the environment, and said Wales could be "a template for sustainable development the world over."
Plaid director of policy Simon Thomas called climate change mankind's greatest threat which "kills more each year than war and terrorism and is destroying habitants, livelihoods and economies round the world."
"The most vital task is to get shoppers and governments to support local producers," said Mr Thomas.
"Shipping in food over long distances from unsustainable farming practices destroys local jobs and the world environment."
Voters were urged to have their say on 5 May as the Electoral Commission's "Do Politics" campaign arrived in Cardiff.
A 10ft tower was erected in the city's St David's centre, where advertising campaign characters Tom and Mike encouraged shoppers to think about the impact of politics on their lives.
Glyn Mathias, the Wales electoral commissioner said: "Voters are given a real chance to show they care about such issues as the food they eat, the air they breathe, or the school they send their children to.
"In 'not doing politics', people are risking their opinions going unheard."