Originally Posted by
ThatT1Feeling
I'm not sure if you can create a PNR just with children in. I can see what you're trying to do, but without paying for seat selection, it's very possible that you would end up with 2 groups of 2 (1 x adult, 1 x child) in different parts of the plane. Clearly if you were booking on one PNR, you could use your Silver benefits to select seats for all of you, but a single PNR isn't possible with some tickets paid with Avios and some with cash.
Couldn't you book all 4 tickets as part cash, part Avios? That might work??
It should be possible when done on the phone, after having already booked the adults. But there is no chance to reserve seats in advance for them without paying... and sincerely I would pay immediately than have to remain uncertain until
very close to the departure date.