I think, in practice, our family does what AGPrincess said 9 times out of 10 anyway. It makes sense to keep the kids with me until we order so that I don't botch it up - but I don't think they should be clogging the line especially since they're not carrying those heavy trays anyway. Once we're past the register, the kids usually grab a table. Since we have more than one child, one is put in charge of doing what Texas lady described - getting the napkins, ketchup packets, etc. When DH and I grab the trays, everything else is already at the table, so we just eat and go.