There is a good, once-a-week immersion program if the child is not lucky enough to enter a full-time program.
EasySpanish123.com is a great resource, with classes on Saturday mornings. The classes are from 9-12 (not just a single-hour tidbit) with a recess and take place in modern classrooms maintained in a church in Tenleytown, DC. Kids as young as 5 are accepted and the teachers are great. Forms a nice basis for later enrollment in a full-time immersion program. I understand there is an open house on Jan 19 from 10-11am.