It depends on the severity. Very disabled children can be absolutely ruinous to the lives of healthy siblings. They can require lifelong institutionalization or adoption by those of competency from an early age as the parents simply do not have the resources, medical or otherwise. That's hard reality.
Children born like this would take extraordinary amounts of energy to heal that are WAY beyond what is imaginable and borderline impossible once they have come out physically. The amount of effort you need to look after cases like this, it's way beyond what regular families can handle, most of these families who can are upper middle class Americans and on a borderline knife-edge with debt. It's not even possible in a lot of countries. Many of these happen spontaneously due to the issues HPS Lydia described meaning people aren't prepared. Xians love these types of beings who can't look after themselves and want to upend society to make everyone pay for them.
Note what I say here: severely disabled as in paraplegic, unresponsive, riddled with extreme health problems, excruciating body/face deformities or mentally retarded to the point where they will never live independently. Not minor autism, dwarfism, deafness, tourette's, manageable disorders of organs or something like this where the person can still have quality of life with adjustments. Giving children up for adoption due to health problems that are manageable is callous and puts unnecessary stress on society, it's more like what Rousseau did in putting four of his healthy kids in an orphanage (where most of them probably died) because he couldn't be bothered.
People with Treacher Collins and dwarfism breed and then make the state pay for endless expensive operations which are also horrendously painful for the child and then the media blares out propaganda about how they are beautiful. This is wrong and also an abdication of proper parental rights, which in this case should be zero outside of maybe adoption. Not everyone should have the wanton desire to procreate just to make people who look like them.
In addition, a very small amount of children have psychological problems and very bad character traits (especially extreme violence) that are way beyond the parent's ability to resolve and don't come from their upbringing at all. They may be a danger to their siblings. They might have to go into care at some point... though this is not good either way.