The Young Runaways (1978)

Heartless parents CL 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