how do I add check boxes in form created with the Registration module?
At the time of Field Creation.

Select FIELD TYPE : List (text)

Select WIDGET : Check boxes/Radio buttons &amp; save


  Allowed values list : 
  
  1|list1
  
  2|list2
  
  3|list3


&amp; save field setting.

You see that radio buttons are shown.

Now in FIELD SETTINGS : Select Number of values : Unlimited &amp; save.