My younger son learned to form his letter correctly on his LeapPad. The Mr Pencil stylus offers a similar experience for kids who have access to an iPad.
The Mr Pencil stylus is much chunkier than the one that comes with a LeapPad though - it's designed to make it easy for little hands to grip.
Learn to Write with Mr Pencil is recommended for children aged 3-6 who are learning to form their letters correctly. I have two young kids and I think this is something it's well worth spending time on. If kids get into the habit of forming letters incorrectly it can be really difficult to fix. It's much better if they form them correctly from the start.
The Mr Pencil app teaches kids where to start each letter and the order to make the strokes in. In covers upper and lower case letters. The app itself is free.
Here's the overview video from LeapFrog:
You might wonder whether kids should be writing on paper, rather than on a tablet. Well, I volunteer at my local school with the younger classes and they use whiteboards a lot these days. They have less friction and make it easier to form letters. Using a stylus on a tablet has a quite similar feel to it.
And as a parent, I appreciate not having my kids use up lots of paper practicing their letters. Working on a tablet is much more convenient.
LeapPad also have other tools for helping kids learn their letters. The LeapReader pen does use paper - it's special paper that makes the experience interactive. And the LeapReader also helps kids learn to read with special books. The LeapReader is the better choice if you want your child to get used to writing on real paper.
There's also the LeapPad range of tablets which use a stylus and touchscreen and have apps and games that teach letter formation and lots of other educational skills.
Buy: LeapFrog Mr Pencil Stylus and App
App Download: Learn to Write with Mr Pencil App