Recently, some researchers claim that exposure for excessive time to touchscreens is harmful for children. According to them, children who frequently use the devices with touchscreen can cause motor delays and/or decreased muscle strength. The American Academy of Pediatrics published a warning that children less than 2 years old should avoid these devices.
Mail Online: Toddlers who use tablets or smartphones may develop long-term problems with their hands and fingers, experts warn
I think it is a pointless question whether touchscreens are harmful for children. It is no doubt that playing with only one tool for an extremely long time is harmful. There are no exceptions; iPad, other gaming, internet, soccer, baseball, and so on. Balanced activity is necessary for developing both physical and mental abilities, especially in childhood. Playing sports is healthy, although excessive training can cause fractures. If you write a lot of letters in a short term, you would suffer from carpal tunnel syndrome.
Actually, human muscle cannot grow up without appropriate exercise. Nowadays, we hardly have an opportunity to handle heavy things. Ancient humans perhaps are more powerful. Instead, we take so rich nutrition that our muscle and skeleton are firmer than our ancestors.
So, will our descendants be not able to handle a pen with a hand in the future? Some Sci-Fi novels describe such aliens who are so weak. It is not a joke. However, I do not know which people are happier.
At least, there are no academic papers to refer to adverse effects of touchscreen use on children, as far as I searched. Indeed, it is difficult to identify the true influence of a certain manner on the development of children. The truth is still unknown.
Overall, it is appropriate not to incline to a certain method to joy a child. Various pleasures should be given to children, not limited to electrics, or athletics.