Yes; but I'm certain you won't get the desired effect, since this servers are managed by different providers - blocking different domains.
Also, here is the correct method (I realized option dns
was a Boolean value):
config host
option ip '192.168.1.2'
option mac '00:11:22:33:44:55'
option name 'mypc'
option dns '1'
option tag 'kids_dns'
config tag 'kids_dns'
list dhcp_option '6,216.239.38.120,208.67.222.123,208.67.220.123'
Hope this helps.