What act in Romeo and Juliet did they have a party for Juliet's Love?

I'm not sure quite what you are asking. In act 1 Capulet throws a party. It is here where Paris has a chance to woo Juliet. Initially Capulet gives his consent if Juliet likes Paris. Ironically at the party, Juliet doesn't fall in love with Paris rather she is smitten with Romeo. I'm not sure how this question relates to children being unwatched. Juliet was very much raised by the nurse. She, however, would have been quite regulated as to what she could or could not do. Romeo, being a boy, would have had much more freedom.