Siblings With Children At Adult Reception

I am including two of my brother`s children in the wedding in addition to two nephew`s on the grooms side. Which leaves.. 5 siblings out.. It is an adult reception. I somewhat feel like the other siblings to should be included. How do i handle this, its not the parents feelings I`m concerned with it`s the children`s feelings. The cost per plates is 50. So thats a pretty hefty price..to pay for a child`s meal.. And if I allow my siblings to bring their children is it reasonable or fair to ask that they be picked up at a reasonable time.. I am just looking for advice on how to handle the matter. The wedding ceremony isn`t till 5:30 pm so that leaves the reception starting at around 7