it is very normal for snails to not eat usual snail-food for a few days after hatching. It is most common for hatchlings to eat some of their eggs and sit there in the soil for a few days. It appears to be of benefit, in terms of the snail's health, to let hatchlings eat their eggs as their first meal.
if they have eaten some of their egg shell they may not need cuttlefish for a little while. They will take it when they are ready. If you still have concerns after a while about their calcium intake then I suggest buying some limestone flour off the internet (horse stores often stock it), as a good alternative to cuttlefish. it may be mixed with the soil for calcium to be absorbed through the foot, or mixed with water to a paste (like mixing plaster) and allowed to dry into blocks.