Tortoises are not social creatures. They are happiest going about their business with all 4 feet on the ground. They don't like being constantly bothered or being picked up too much. They don't want company, especially from other tortoises. Another tortoise is simply competition for territory and food.
Keep a tortoise for the children to grow up with by all means. My husband was 7 when Joe came into his life 47 years ago and our children, now in their 20s, grew up with Joe. But don't have expectations of the tortoise being company, a play thing or something to take to show and tell at school. It's more something to care for and watch.
As for species, even the smallest need a minimum of 4'x6' (1.5 x2.2 metres) once they stop being babies after the first couple of years. Good beginner tortoises are the Testudo (Greek, Hermann's and Russians) as they are more straightforward to care for.
I agree that tortoises don't like being handled too much. But most get used to their keeper.
On the other side, tortoise live 55 years to over 100 depending on the species. A child's attention span is a lot shorter than that.
Whatever type you decide on we will help you get the enclosure(s) ready and help you avoid spending money on pet shop products that are not any good.