My oldest first went into a toddler bed at 17 months old so a bit older than your LO, but I just kept putting her back in bed with no fuss. You could try thaht. She wasn't upset or crying, just finding it fun to get up, so the first time she got up I told her it was time to go to sleep, night night, gave her a kiss and tucked her in etc. The next few times I said something like "sleepy time now, night night" and quickly tucked her in, then for the few times after that it was "Go to sleep" (not shouted, said nicely!) and after that I just put her back in bed without talking. The first night it took something like 45 goes to get her to stay in bed! I just waited outside her bedroom door, which was open, until I saw her get out of bed. If she was just sitting up I left her. The second night it was around 18 times, the next night 3 times, then after that she just stayed in bed. If she cried, which she did once or twice on the first night, I gave her a cuddle until she calmed down but no real talking, then carried on. It was very stressful on the first night wondering if she'd ever stay but after that it was easy and worked pretty quickly.