Two-year-old Loui Legend, from Brighton, has Treacher Collins syndrome, which affects the development of the bones and tissues of his face.
He was chosen as a brand ambassador for Lulas Dudes & Dolls after his mother Karly Herriott sent in a photo of him wearing one of its products.
The company has also made T-shirts to help fundraise for operations he needs.
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Loui's condition is so severe that he has to have a tube inserted into his windpipe in order to breathe, and he is fed through a naso-gastric tube.
He also has to wear a bone-anchored hearing aid on a headband to be able to hear, and is unable to speak.
Loui requires 24-hour care and faces a lifetime of hospital trips, procedures and operations.
His parents have been raising funds for specialist operations which would improve his quality of life, but are only available in the US.
The condition is also called mandibulofacial dysostosis, and it affects the head and face.
It is believed to be caused by a change in the gene on chromosome five, which affects facial development.
Characteristics include:
Most children with Treacher Collins have normal development, but benefit from early intervention speech and language programmes.
Source: The National Craniofacial Association
A toddler born with a rare genetic condition has been picked to model for an online children's clothing company.