Often raise them as normal and add an extra BB for every limper to the raise size.
Low pocket pairs (22-66) can sometimes be best to just limp in after others. In late positions, limpers give you a chance to see a cheap flop with Axs, Kxs, and suited connectors that you normally may fold.
If the limp-reraise it's often a VERY strong hand, so re-valuate pot-
odds, etc if that happens.