I have new born cub and I need it to follow me but when I leave my den it the only one that doesn't...

You need to kill a small animal then carry it to your den to feed your cub. To carry it, you need to go on the dead body and press on the attack button ( the button you usually use to hurt your preys ) then you should grab the dead animal. Hope this was helpful !

The pup has to be level 2 before it can leave the den. It's why you start out at level 2.

Hope this helps!

When the pup isn’t a new born it can’t follow you so you have to hold the food and run or tp to your den and let it eat

When it is new born you need to first bring it food because it can't leave the den, you can only pick up small animals like rabbits, hares, skunks, and raccoons. You pick them up by hovering over them and pressing the fight sign. Once the baby levels up it can leave the den and it it levels up again it can fight and you can play and upgrade it.