I do not know what is on line these days.
There is a book which covers the various approaches to ground work.
Bayley,
Groundwork Training for Your Horse: Develop a Deeper Bond with Your Horse Through a Range of Exercises and Games.
It is a sort of anthology of the trainers working at that time. I read it but the Amazon review points out it covers many traners.
"None of them are treated in extensive detail, but there is enough there to try things out & consider if that approach is right for you and your horse."
I preferred to buy the books by the individual trainers.
My own awareness of ground work started with a couple of leaflets by Kelly Marks. Most NH (Behaviouist) trainers at that time were American and used a round pen. Kelly Marks was a student of Monty Roberts much in the UK news then as he had spent time with the Queen and her horses. She explained how one could do the same type of work in a field or inside a stable.
I did not care for Monty Roberts technique of sending away nor his Dually headcollar when it was used as a tightening halter but their Intelligent Horsemanship organisation helped a lot with home visits to UK people who could not control their ponies.
I also had some vids from a trainer in Sussex (Sue Gardner) and paid for a lesson with her but she never let me inside the school. I also went on an IH training day with unpleasant instructors.
I could not sample Parelli as it was at that time only for people who owned a horse but my grand daughter had some parelli style groundwork lessons.
As I cant ride at the moment I plan to do some groundwork with Ella next week. Apart from leading and halting and backing up, most early groundwork invoilves getting the horse used to passing over or between obstacles. But the exercise that stays in my mind (after the simpler stuff) is one that obliges one to control each foot of the horse individually. One lays out 10 poles in an S shape. One leads the horse through this, step by step, without letting it step outside the poles. It involves two left turns and two right turns for the horse.
Nothing I have cited here relates to a very young horse. You would need to check one of the books on training young horses to make sure nothing I have mentioned (like the maze exercise) would be bad for the horse. Rashid trains young horses in the context of what you need to do with a young horse. That is it must be caught, led, tied up, stabled, possibly loaded onto a lorry or horsebox. It must lift its feet. It must accept being groomed and touched all over. And it must be taken back into its field and released without injuring the handler. He uses long lines in preference to lunging on a circle.
A book re;ated to IH which I liked very much though it is not instructional was
Whispering Back: Tales From A Stable in the English Countryside
by Adam Goodfellow and
Nicole Golding which is now only £2,99 on Kindle and you might enjoy it.
Well that is my essay done for the day and I should have been working.