It's possible, depending on how severe his condition is and whether your family is income-eligible for the program. For a child who sees two therapists a week, it's worth investigating the possibility. See http://www.ssa.gov/disability/disability_starter_kits_child_eng.htm for more information. You may wish also to consult with an attorney in your area.
In addition to disability issues, there are financial concerns. SSI is a need based program, and that means they look to all income coming in to the house to decide what amount will be paid if the child is disabled. Talk to your local SSA office to see if you are even eligible. If so, file right away - benefits cannot be paid until the start of the month after you apply, so each month you wait, you risk losing benefits.
Good luck to you
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