recursive_schema.rb

require 'dry-validation'

class Schema < Dry::Validation::Schema
  
  group :node do
    key(:name) { |name| name.str? and name.filled? }
  
    key(:children) do |children| 
      children.array? do
        children.each { |child| child.group?(:node) }
      end
    end
  end
  
end

schema = Schema.new
puts schema.call({
  name: 'Right',
  children: [
    {name: 'Right Son' children: []},
    {name: 'Right Daughter', children: []}
  ]
}).messages

# => []

schema.call({
  name: 'Wrong',
  children: [
    {name: 1, children: nil},
  ]
}).messages

# => [... one of the children does not comply with the rules]