All my children have two names. If you count the syllables, the first born has 1+3, the second 2+2 and the 3rd 3+1. This was not intentional in any way, but is presumably something to do with how long a name 'feels right', with the correlation of birth order and first name length entirely coincidental.

I suppose we could have still fitted the system if we'd had a fourth, but fifth would have been a bit of a challenge.