The Young Runaways (1978)

Heartless parents C.L. Doyle and his wife take two of their older children, Rosebud & Joseph T. Doyle, on a family vacation to Alaska, but dump their younger ones, Freddy & Margaret Jean, in a Los Angeles foster home. Infuriated by this, Rosebud talks Joseph T. into running away with her so that they can break their younger siblings out of the system, which sparks a manhunt, and an outburst of sympathy among kids everywhere.