Applying for visa for child at same time as spouse visa

Hi . I am a british citizen looking for some advice on which uk visa for a child aged 5 to come to the uk permanently
My ukrainian wife has just applied for a uk spouse visa and we want to apply for her . our son to come with us . I adopted him in ukraine , but this is not recognized by the uk .
I thought we would apply under the children of british citizens group , as he his my stepson under uk law . But it says both parents must be settled in the uk to apply here , and as my wife as only just applied for spouse visa , she is not settled .
I have looked at all visa groups on ukba website , but can not find which visa to apply for . Any help would be great . thanks Tim

See also Children of British citizens and settled people.