Can I buy an adult fare with miles and pay cash for a child?

Not sure how this works so forgive me!

I want to book for MCO next year. I was going to book two economy seats and hope for an upgrade using my miles but I think, on that route, that I'm not likely to get one.

So I was wondering, can I book my fare using my miles - I have the 100k needed - and book my son's separately and pay for that? How does it work?

Thank you!!

Not sure how this works so forgive me!

I want to book for MCO next year. I was going to book two economy seats and hope for an upgrade using my miles but I think, on that route, that I'm not likely to get one.

So I was wondering, can I book my fare using my miles - I have the 100k needed - and book my son's separately and pay for that? How does it work?

Thank you!!

To execute a move like this you'd be best calling VS to ensure you end up on the same PNR. More importantly though your use of the 100K miles depends on the availability of reward / upgrades as all miles seats (be they fully funded or part funded by miles) come out of the same pool., so if the website is showing / the agent is reporting no upgrade availability you won't, I'm afraid, be able to use your miles to fully "pay" for a ticket.

It obviously depends on time of year, but I have managed upgrades to Upper on the LGW MCO route three times.
Out in Feb, back in March.
I do it by buying my tickets at the first opportunity and checking for reward seats on a daily basis.
Although I've not done it, you may find Heathrow to MCO via Atlanta gives more chance of an upgrade.

Best of luck.
Dick D