Travel During MN1 Application without visa

[Grapheler]

Hi All,

I am looking to travel to France with my family in a fortnight, and have not yet received my sons Naturalisation certificate to do so after 3 months waiting
Our situation...My Partner and i have both recently settled on ILR, but our son does not have a visa as we thought it best to just wait and get his naturalisation through MN1 section 1(3), rather than pay for a visa, as the timelines are the same, and we weren't planning to leave the country during this time.

We applied using the NCS Service at Wandsworth, so he has his New Zealand Passport to travel. My question is will get back in without a valid visa during his application process? Also will this void the application?

Thanks for your time, and consideration. I looked at heaps of other posts, but couldnt see any where the kid had no previous visa.

Cheers