ژ is the rarest letter in the Urdu alphabet. Only a handful of common words use it, almost all of them borrowed from Persian or French through Persian. A child can finish school reading Urdu fluently and meet ژ only five or six times in real text. Teach the shape and sound for completeness, but do not drill it the way you drill ب or س. The honest pedagogical message is that this letter exists, it has a soft buzzing sound, and you will recognise it when you see it. Stroke timings approximate.

Tell your child that ژ is the alphabet's quiet guest. Most words do not need it; a few specific ones cannot do without it. Knowing the rare letters is part of knowing the language fully.