MPs have warned that school trips were being restricted to pupils from wealthy backgrounds as ministers had failed to address teachers' concerns over health and safety.
The Children, Schools and Families Select Committee said the "steep decline" in the amount of time children spent outside was "shocking".
In a new report - Transforming Education Outside the Classroom - the cross-party group of MPs urged ministers to ensure school trips did not become the preserve of pupils from private schools.
Health and safety concerns from state schools had been a "significant barrier to school trips" and had yet to be assuaged, they said. The Government was urged to publish guidance "at the earliest opportunity".
The report said: "The delay in getting revised health and safety guidance in place is disappointing. Without a further drive to both ease concerns about litigation and root out the use of health and safety as an excuse for curtailing provision, the effort and funding that has been put into promoting learning outside the classroom will be wasted."
The MPs suggested that all pupils should be entitled to at least one school trip each term under the national curriculum. They urged ministers to provide enough funding to support learning outside the classroom and said even a "small sum" would make an "enormous difference".
Labour MP Barry Sheerman, committee chair, said: "The steep decline in the amount of time children are spending outside is shocking. Research has shown that the likelihood of a child visiting any green space has halved in a generation.
"It is vital for the Government to make a commitment to a serious funding increase to ensure that all children have opportunities to visit the wealth of museums and galleries, and the natural environment of the English countryside, which are at our disposal."
The report also recommended that low-income families be given subsidies so that poorer children would be able to afford to go on school trips. It said: "Learning outside the classroom must not become only the preserve of pupils from more affluent backgrounds or from the independent schools sector."
The MPs acknowledged that the Department for Children, Schools and Families had set up the independent Council for Learning Outside the Classroom in 2009, but said concerns continued over the Government's support for school trips. The committee suggested that education watchdog Ofsted include the provision of school trips in its inspections. And new teachers should be exposed to learning outside the classroom early on in their career, giving them the skills and confidence to lead school visits.