to paraphrase (and to simplify to the case of 2 inputs), your problem is that:

runApp(list(
    ui = bootstrapPage(
        textInput(inputId="xlimitsmin", label="x-min", value = 0.0),
        textInput(inputId="xlimitsmax", label="x-max", value = 0.5)
    ),
    server = function(input, output) {}
))

shows

But you want side-by-side small inputs, like so:

The short answer

textInputRow<-function (inputId, label, value = "") 
{
    div(style="display:inline-block",
        tags$label(label, `for` = inputId), 
        tags$input(id = inputId, type = "text", value = value,class="input-small"))
}
runApp(list(
    ui = bootstrapPage(
        textInputRow(inputId="xlimitsmin", label="x-min", value = 0.0),
        textInputRow(inputId="xlimitsmax", label="x-max", value = 0.5)
    ),
    server = function(input, output) {}
))

gives:

The long answer

Side-by-side inputs

Let’s do side-by-side first:

Currently textInput generates two separate tags – the label, and the input, each of which is configured by CSS as display:block, which means it’s a rectangle that will break to the left side of the container. We need to wrap each textInput‘s field in new container (div) and tell that container that the container that follows it (the next textInput) is allowed to be on the same horizontal row on the page, using CSS’s display:inline-block.

So we add a div with a style around each textInput:

runApp(list(
    ui = bootstrapPage(
        div(style="display:inline-block",textInput(inputId="xlimitsmin", label="x-min", value = 0.0)),
        div(style="display:inline-block",textInput(inputId="xlimitsmax", label="x-max", value = 0.5))
    ),
    server = function(input, output) {}
))

Small inputs

Now let’s deal with small. There are a few ways to do small,

1. make the font smaller,
2. make the input box have fewer characters in it.
3. tell css or (here) bootstrap to draw a smaller box

Since bootstrap.js is really in control of layout when we use shiny, only 3 will reliably work, so let’s use that.

Input sizes are documented in Bootstrap 2.3.2’s CSS Forms documentation, under ‘Control Sizing’. It includes a variety of sizes from mini, small, medium, large, xlarge, and xxlarge, and the default is probably medium. Let’s try small, instead.

To set the size, we need to change the class of the input tag generated by textInput.

Now textInput is just a convenience function around the more powerful tags functions such as tags$label and tags$input. We can build a more powerful version of textInput that allows us to configure the elements, specifically the class of the input node:

textInput2<-function (inputId, label, value = "",...) 
{
    tagList(tags$label(label, `for` = inputId), tags$input(id = inputId, 
                                                           type = "text", value = value,...))
}
runApp(list(
    ui = bootstrapPage(
        div(style="display:inline-block",textInput2(inputId="xlimitsmin", label="x-min", value = 0.0, class="input-small")),
        div(style="display:inline-block",textInput2(inputId="xlimitsmax", label="x-max", value = 0.5, class="input-small"))
    ),
    server = function(input, output) {}
))

And we are done – but we can roll some of this functionality up by having textInput3 generate the div tag. It could also set the class by itself, but I’ll leave that for you to write.

Wrapping it up

textInput3<-function (inputId, label, value = "",...) 
{
    div(style="display:inline-block",
        tags$label(label, `for` = inputId), 
        tags$input(id = inputId, type = "text", value = value,...))
}
runApp(list(
    ui = bootstrapPage(
        textInput3(inputId="xlimitsmin", label="x-min", value = 0.0, class="input-small"),
        textInput3(inputId="xlimitsmax", label="x-max", value = 0.5, class="input-small")
    ),
    server = function(input, output) {}
))

For interest’s sake, here’s the version using class input-mini: