So here is what I, me, personally, would do:
You and your son stand at A60, with your husband behind you. As you approach the boarding agent, literally say “we have A57 and A60 and would like to use family boarding to board with my husband who has B02”
They might wave you all through with the As. They might start family boarding right there, with your group as the first group. Either way, you are doing the correct thing and boarding with the worst number (in this case superseded by family boarding) rather than asking for a special exception for everyone to board in the As.
It’s splitting hairs, but I’m cognizant that these employees get asked to many special exceptions so many times every single day and are likely so sick of it.