How can I reserve seats for children under 2 if there is no charge for them?

You need to call them for that information

If they need a seat you need a ticket

I don't think you can reserve seats like that. The best thing to do is just get there early to make sure

I'd call

I think any child under 2 is considered a lap child so they wouldn't need a seat to reserve kind of like if you were in an airplane