My neighbour converted to Islam when she married, but she does not behave like a Muslim. Should I tell her this since my concern is the kids?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

The religion encourages sincere well-wishing for every Muslim, as reported in a Hadith in Saheeh Muslim.  Sincere advice should be given in a soft and pleasant manner.  The purpose behind this act should be to bring good to the person.  There are many good ways to perform this act such as offering an Islamic cassette or a useful booklet, etc. that treat his/her situation to the person.

Allah knows best.