Nick Clegg has pledged to protect education spending on children and teenagers "from cradle to college".

Unveiling the first commitment of the Liberal Democrat manifesto for next year's general election, the deputy prime minister pledged to protect an extra £10bn of education spending on top of commitments delivered in this parliament by the coalition.

Clegg said: "Any parent knows that a child starts learning from the moment they are born and carries on learning all the way into adulthood. We have invested in early years because if a child starts behind the chances are they stay behind."

The current protected spending commitments are the £36.6bn dedicated schools grant, the "basic building block" of funding for five- to 16-year-olds, and the £2.54bn pupil premium, which targets help at pupils from disadvantaged backgrounds.

The Lib Dems will pledge in their manifesto to extend the ringfence to the early years block of the dedicated schools grant. This includes the commitment to offer 15 hours of free education provision for three- and four-year-olds, the new early years pupil premium and the new free education entitlement for two-year-olds from the poorest 40% of households.

The ringfence would also protect the Department for Education budget for 16- to 19-year-olds. The newly protected spending would amount to £10bn, comprising £7bn to 16- to 19-year-olds and £3bn to early years.

Clegg said: "I believe we now need to go further than the current protections for our schools. I can announce today that in the next parliament, Liberal Democrats will go further by protecting the full education budget, not just five to 16, but covering children from the age of two to the age of 19 – from cradle to college.

"The Liberal Democrats don't just want more money for education for the sake of it. We believe education should be properly funded because education is the very core of a liberal society. Money invested in our children is the best investment of all because education really can transform lives."

He added: "This is a significant extension of the ringfence, the protection. Crucially, it builds on a lot of the spending decisions we have already taken in this government … It would be unimaginable for us as a country, having made those steps to invest in early years education, to reverse that. Far from reversing these changes, we want to build on them in the future."

The deputy prime minister admitted that the Lib Dems would have to make spending cuts in other areas to fund the new pledges. He said the party would spell out its wider spending plans more clearly closer to the elections.

Clegg set out his overall fiscal approach last week. This involves sticking with the timetable agreed with the Tories to eliminate the structural budget deficit by 2017-18, though the Lib Dems plan to achieve this through a mix of further tax increases and further spending cuts, whereas the Tories would use only spending cuts.