The amount of federal money going to families with disabled children has surpassed traditional welfare programs as a source of income over the past two years. Roughly $20 billion was spent by the children’s Supplemental Security Income program, about $2 billion more than other welfare programs. Analysts say that the program has become an access point for families that lost benefits in the welfare overhaul of the 1990s. It started in 1974 as a small program serving families in which parents could not work because they had children with severe physical disabilities. The program has doubled its number of recipients in the past two decades, and now serves 1.3 million youths with behavioral, mental, or learning disorders, including harder-to-assess conditions such as ADHD. Its defenders say it is one of the last programs for the poor that hasn’t faced severe cuts from Congress.