Show correct header on child name page in clinic booking

The heading text and the caption vary based on number of children and the number of the current child. The previous code worked fine locally, but initially had both of those values still set to zero on Heroku resulting in being asked for the "next child" on the first time through. As I couldn't quickly work out why the values weren't making it through (logging showed they always were coming through, on localhost), I've changed the logic slightly to avoid obviously wrong text in the page title.

Author: malross

app/views/book-into-a-clinic/form/child.njk

@@ -1,6 +1,6 @@
 {% extends "_layouts/form.njk" %}
 
-{% if childNumber == 1 %}
+{% if childNumber < 2 %}
   {% set title = __("clinicBooking.child.title.first") %}
 {% else %}
   {% set title = __("clinicBooking.child.title.next") %}