Very difficult for 18 month old

I purchased these for our 18-month old daughter to help with fine motor skills. We used to have the Melissa & Doug brand eggs about 4 years ago with my oldest who is now 5 year old and she loved them however these eggs are VERY difficult to pull apart. I even have to work to get them open at times. My toddler tried a couple of times and ended up throwing the eggs, so we have put away and will try again in a few years.
I will say, they have a very sturdy case made of thick plastic and colors are vibrant, shapes are all different which is all a plus, however they are just too hard to pull apart.