Sometimes you will have a situation where a younger sibling or child wants/is appointed to the role of Maid of Honor. This is in title only. And they should not be expected to handle and of the planning.
Typically, the Maid of Honor takes on most of the planning for the bachelorette party and bridal shower, gives a speech at the wedding and helps with a lot of the wedding planning/prep. It’s a lot harder to have multiple bridesmaids take on all those duties while they have different schedules/commitments.
It’s completely ridiculous to think that a child could do any of it.
This is different, however, if it isn’t the first marraige.
Second marriages are usually a little more toned down and it was probably important for them to include their children.