Bus drivers have apologised for insisting on charging adult fares for a child of 11.
Jasmine Brakes was told twice she wasn't entitled to the cheaper junior ticket unless she could prove she was under 17.
Her mother Donna has complained about the incidents, which she says embarrassed her daughter.
Mother-of-five Donna said: "If my daughter was 14 or 15 I could see their argument as teenagers might try to pull a fast one. But there's no way she looks that age. I think it's ridiculous."
Jasmine had boarded a Number Seven from Brighton station with her grandmother to visit her aunt when she first encountered problems.
The driver asked for proof of Jasmine's age, which she did not have.
Despite protestations from her grandmother, the bus driver insisted Jasmine pay the full adult fare of £3.20 for an all-day pass. The family reluctantly paid for the ticket, which should have cost no more than 80p.
The next day Jasmine, of Myrtle Road, Lancing, boarded a Number One at the station with her grandmother. Again, she was asked for ID and was again wrongly overcharged, this time for an adult City Saver Fare of £1.70, twice the amount she should have paid.
Mrs Brakes said: "Jasmine wasn't with a bunch of friends trying to get a half price fare. She was with her grandmother. It embarrassed her and made her feel like they were calling her a liar. At 11 you're only just starting to grow up and you've got people looking at you on the bus thinking you're trying to pull a fast one.
"They want people to use buses but they've almost made us look like criminals because of their heavy-handedness over ID cards. I'm absolutely disgusted with the service.
"I don't see why Jasmine should get an ID card just to prove she is 11 when she clearly looks 11. I would consider getting her a pass when she starts going out alone in a few years time but it's just not necessary when she is travelling with the family."
Brighton and Hove Bus and Coach Company, which run the two services, has apologised to the family for the error.
Managing director Roger French said ID should only be requested for young people aged 14 to 17. He said: "This customer was charged an adult fare which was wrong and we are very sorry that happened.
"But, the customer would have made an even greater saving had she had an ID card and could have travelled for as little as 20 pence."
The firm has offered free tickets or a refund for the additional cost of travel the family incurred.
But, Mrs Brakes said it did not compensate for how the family were treated.
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