My DD is 20 months and we've had this lately too. She has previously been a marvellous sleeper, often going for 12 hour stretches with not a murmur.
She's very aware now, so I don't want to start letting her into our bed, as as soon as she's there she thinks it's playtime.
I just go in if I hear her crying, check she's covered over (we wondered if she'd been waking because she was cold), give her dummy back, and get her some warm milk once if really upset. A friendly but firm 'it's sleep time now' with no eye contact so she knows we mean business. Sometimes she cries/whimpers for a while, sometimes she has a play with her teddies and we hear her chatting but we don't go back in, and more times than not, she goes back to sleep by herself.
We got caught up a few weeks ago with pandering to her (she'd deliberately throw her dummy out, ask for more milk, say she'd done a poo, say something was sore etc etc) but they were just tactics to make us keep going back to her so we stopped that.
Obviously if she'd had a nightmare etc and was more upset than the usual whimpers, I'd reassure her with cuddles etc but we haven't experienced anything like that yet.