I only have 1 kiddo... So I wouldn't send her through a queue alone and wonder if she'd be seated with strangers... But if I had 2 kiddos then I'd be okay-they'd look out for each other and be together through the whole ride... When you get up to the front you tell them you are (two) people, and they'll put them together... Of course assuming that they are well behaved, not mischievous or have some sort of disability that would hamper their overall safety.
This exactly what I'd do. The year our kids were 7 and 9, we visited Disney for the first time and we also went to Canada's Wonderland (an amusement park). In both cases we let our children go through lines for things we didn't want to ride together (they had more of a taste for coasters than we did). My husband and I believe very strongly in preparing our children for independence.
With this in mind, our children knew to stick together. They knew what to do if they got lost and couldn't find us. They knew what inappropriate behaviour looked like from an adult. They knew not to blindly trust or obey a stranger. They knew how to pick a "safer stranger" (a cast member in uniform, a mommy with kids, a daddy with kids, someone working at a cash, etc...) if they needed help from an adult. We let them know that we trusted them to be intelligent and demonstrate common sense in difficult situations. They've never failed to live up to our highest expectations.
The ONLY time I felt at all nervous was when they were running all over Tom Sawyer Island. It seemed very large, the tunnels were dark and twisty, and I couldn't see them at all. BUT, we'd told them to meet us a specific spot at a specific time, and they did just as they'd been told.
So I'm glad I was able to push past my fears and give them that freedom! They proved to me once again that they were becoming capable, reliable young people.
I have to say, too, that these early lessons (however scary it sometimes was for me as their mom) have really paid off in a positive way now that they're teenagers. (I say this as I'm waiting for my 17yo to figure out how to get back from her statistics course on the other side of the city, periodically sending me updates on her adventures on public transit. Apparently she's found another girl in the same boat, and they're working it out together!)