Pupils from Longford Community School, The Heathland School and Hounslow Manor School were joined by conservationists from Sky's The Bigger Picture.
They planted English oak, silver birch, sweet chestnut and wild cherry, said Sara Dawson, a co-ordinator from Sky.
Once a tree-filled royal hunting ground, most of Hanworth Park's trees disappeared in the World War Two to make way for a makeshift airport.
It became a park after the war, but without its trees.
The three-year Hanworth Park Urban Forestry Project was led by several groups.
These include eco-charity Green Corridor, which secured funding from BAA Heathrow. Charity Trees for Cities, London Borough of Hounslow and the Friends of Hanworth Park are also taking part and will plant 30,000 new trees by 2010.
"The trees will re-establish woodland copses and avenues, creating a parkland similar in feel to that of Richmond Park," said Sara Dawson.
Graham Simmonds, chief executive of Trees for Cities, said: "Hanworth Park sacrificed its trees for the war effort and we're restoring it to its former glory."