In the first part of the article, which is the collection of the educational software, GCompris and KDE Educational Suite are complimentary programs, rather than competitive; they have some parts in common but most are different. If you have free space on your hard disk, I recommend you install both suites. Etoy's targets a little older children but is a good base for developing skills for the long term.
The second part is actually a compilation of games, without the educational emphasis. The games are smooth, cute and appropriate for children; both in terms of game play and graphics.
Of course this is not an exhaustive list. You can find more programs on the Internet developed with children in mind. Our top ten list has applications that have lasted over the years.
You will be able to find almost all of the programs above and possibly many more in your package manager, which you will be able to install with one click.