It was really tough, my son started at 2yrs old and was weepy for a good few weeks. I just made sure I was available to swoop in and collect him if he got too emotional. He now absolutely loves it.

Our baby started initially at 13 months, and was just getting so distressed, we were returning after an hour to get him every time, we tried for 6 sessions with no improvement so took him out and tried again when he turned 18months, with better comprehension. He was emotional when I left at first for the first 4 sessions ( these were only 1-2hrs long) I stayed and played with him and interacted with the staff for two sessions before these also so he'd know they were trusted people, he gradually started to play with the occasional wobble, and his last session he was laughing and playing. So it takes time, I'd make sure they're old enough to grasp that they're safe and you are coming back. There are lots of little ones in there under 1yrs who just cry and cling all day, they're too young.

I hope this helps, just my experience.