Normal drop off behavior?

I have a group of five 13-18month olds. They are all very settled in and calm and happy for the most part. I have a 15month old that after being here for about 2 months (with a very easy transition) started this phase where she bawled as the parents of all the OTHER child left each morning. Like it was traumatic to watch them to go up the stairs and leave. I'll note she didn't do this for HER parents. The other parents all found it odd and a bit humorous that their kid was fine with them leaving bit this other kid was upset. That lasted a few weeks and now she could care less.

BUT now my 18month old is starting the exact same behavior. Is fine when his parents leave but bawls when the others leave. It only lasts a few minutes then is back to playing happily. It's not fake crying, it's real crying and tears.

Is this normal? I find it quite odd! With the 18month old I am ignoring it and making him move away from the gate and telling him to go find toys to play with.

I assume they know that mom/dad went up that way and the other parents going that same way is reminding them of it and they wasn't to go up and see if mom/dad are there?

Anyone else experience this? I just find it funny that they don't do it when their own parents leave.

Yes I've had a couple of dck do the exact same thing right around the same age you described! It definitely is pretty odd but the phase doesn't usually last long anyways. I think it's like you said; watching the parents leave reminds them of how THEIR parents also left even though at the time they didn't react...lol it's so weird!