I think choosing your words is key!
If there is something that you feel needs to be addressed- approach it differently. Not so much as a possible learning problem but that you want to bring to their attention a behavior that you want to work together on with them.
eg. Not listening to commands sit, come here- they can say it's a normal kid/toddler response but then say he/she isn't looking at you when you get down to his level and these are requests that he/she has to listen to as the rest of the kids do...yes they are a toddler but it's our job to teach them life skills ~ ask how they handle it at home and tell them that you want to brain storm on ideas on how to correct it. When it isn't happening...might open their eyes if in fact the little one is having a genuine, not just a toddler, problem. ???
No parents want to hear that their child is anything but normal.