I'm trying to model a "parent" "children" relationship on Solr but I'm struggling to find a way to get the children documents ordered in some way. The basic query is:

q={!parent filters=$childquery which=document_type:product}
childquery=document_type:sku
fq=category:2
fl=*,[child childFilter=$childquery limit=-1]

and the result is similar to the following (I've cut attributes to be short). I would like the "skus" to be shown ordered by the field "rank" but I can't figure out how to set properly the "sort" parameter. I've tried sort=childfield(rank) but I get only the parents ordered.

Any help will be appreciated.

{
        "id":"0RB2140",
        "document_type":"product",
        "category":"2",
        "skus":[
          {
            "id":"0RB2140 901   54",
            "document_type":"sku",
            "rank":4
          },
          {
            "id":"0RB2140 901   58",
            "document_type":"sku",
            "rank": 1
          },
          {
            "id":"0RB2140 901   60",
            "document_type":"sku",
            "rank": 5
          }
        ]

 }