Accompanied children aged 8 and above are now able to use UK eGates.
Millions more families will now be able to use the gates, speeding up journeys over the summer holidays.
Children over 8 will now be able to use the gates if they are travelling with an adult and are at least 120cm tall.
There are more than 290 eGates at UK airports and ports.
Minister Alex Norris, Minister for Border Security and Asylum said: "Today’s change will make journeys easier for families with small children and reduce the hassle of travelling home after a holiday.
"It will also free up more time for tourists to enjoy our fantastic country this summer and in the years ahead."