As your son is 2 years old and your other seats are not next to each other, they can't even suggest that you allow him to have one of your reserved seats. They will have to allocate him a seat next to one of you - he is too young for Skyfliers Solo.

If you can't put him in 10b at OLCI, just hand him to cabin crew when you board, explain what happened and take your seats. Let them sort it out.

PS - you can book the 2-4-1 for your wife and son online - just select the right people from your household account (and keep reselecting them at each stage, otherwise it will reset it to you plus someone else). You do end up with 2 PNRs though these days (if using miles for all bookings, it used to be possible to get them all on one PNR - now when you try that it forgets the 2-4-1 discount and charges the full miles allocation).