Shorebirds, like wild birds generally, are hard to approach closely. They are wary of large creatures pointing ominous-looking cylindrical objects at them.
First, it’s best to get down to the birds’ level. This not only makes it easier to approach them, it also makes for more pleasing composition (this is true for ALL animal photography, actually). For shorebirds, one might consider actually getting down on one’s belly and kind of crawling towards the birds. Wear clothing that you can afford to get dirty :-).
Second, apparently shorebirds are more leery of creatures approaching from the shore than those which might approach from the water. Photographers have had success actually getting into the (shallow) water and approaching shorebirds from that side. Dress appropriately, of course.
Finally, move sloooowwwwly and take time. Be patient! If you stand or better yet, sit motionless for a long time the birds get used to your presence and might either allow a (slow) closer approach or else in some cases they might even move closer to you during the natural course of their feeding.