Little Lucas Brand will turn three in June, yet a mystery condition means the Sheffield toddler weighs less than 13lb and fits clothing designed for three-to-six-month-olds.
The youngster's undiagnosed genetic disorder also means he cannot yet walk or talk, must be fed via a machine and has a weak immune system making him particularly susceptible to infections.
But despite these challenges and frequent hospital visits, his mum Danielle Eyre says he remains one of the cheeriest and most good-natured youngsters you could hope to meet.
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His plight has touched the hearts of strangers, who are staging a charity football match to help fund a dream trip to Disneyland for Owls supporter Lucas and his family, who live on the Wybourn estate.
Fans of Sheffield Wednesday and the Blades will battle it out on Sunday, May 27 to help raise £1,200 towards the holiday of a lifetime.
Danielle, a clinical support worker at Weston Park Hospital, said: "Lucas is so small his one-year-old sister Isla towers over him. They've performed every test the NHS can offer and they still haven't been able to diagnose his condition.
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"The hardest thing is not being able to get a name for this syndrome and not knowing the answer when people ask if he'll grow or be able to walk.
"But he's the happiest little boy you could ever come across and he's absolutely obsessed with Toy Story so going to Disneyland would mean so much to him."
Danielle Eyre says she and her partner Luke, who is a sales consultant, are 'lucky' to have such supportive friends and family.
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The fundraising appeal and charity football match have been organised by Bradley Marshall, who heard of Lucas's story as his partner works with Danielle, and Danielle said he had been 'unreal'.
Bradley said: "I think the family completely deserve a break from the hard routine they currently live under, and Lucas is a huge Disney fan too, especially when it comes to Toy Story.
"They are also huge football fans, which helps, and with Lucas's smile how could you not want to help?"
The Owls fans v Blades fans charity match will take place on the bank holiday Sunday, May 27, with kick-off at 3.30pm and tickets priced £5.
* For more details about the match, visit www.facebook.com/events/591049727960948/.
* To donate, visit www.justgiving.com/crowdfunding/sendlukastodisneyland.