When inflectional nūn is removed, the remaining ending still identifies the addressee.
لَا تَقْرَبَا هٰذِهِ الشَّجَرَةَ
Do not approach this tree, you two. The dual nūn has been removed; final ا remains.
لَا تَقْتُلُوا أَوْلَادَكُمْ
Do not kill your children. The masculine-plural nūn has been removed; final وا remains.