Under new plans unveiled on Monday, ordering the travel document for youngsters by post sees the price pushed up by £46 to £58.50.
And adults one the same way will see the cost jump from £72.50 to £85 – a 17% increase.
But passports requested online will only rise by £3 – the rate of inflation.
That will see children’s passports climb to £49 and £75.50 for adults.
The measures were suggested by Government ministers to encourage people to apply online instead.
They will have to be approved in a vote by MPs in Parliament before coming into force.
Home Office minister Caroline Nokes said the crackdown was to heap the cost of processing more-expensive postal requests onto applicants, rather than taxpayers.
She announced: “Our priority is to ensure that UK travellers have a secure, effective, and efficient service from the point of application to the time they pass through the UK border and it is only right that we should look at this whole process when setting our fees.
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“These proposals will ensure that those people who don’t travel abroad are not footing the bill for those who do.”
The Home Office said the proposals are not related to the reintroduction of blue passports after Brexit, which will not bear a further cost.