Naturalisation application with children biometric query

Hi, first time, sorry if I am posting in wrong place
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Applied online for naturalisation July 2020 for my two kids aged 5 and 3 n half in the same application like added my second one in the same form.

August 5th, received invitation for biometric for my 5yrd old, but didn't receive any invite for my second son, wonder why, since applied in the same form how come he dint receive any invitation, hence waiting, anyone can say why is this could be?
Thanks
Riaz

Children under 18 applying for registration as a British citizen must also enrol their biometric information. Children under the age of 6 do not need to provide fingerprints, but must have a digital photo taken of their face

https://assets.publishing.service.gov.u ... on-6.0.pdf