The evidence suggests that children younger than two generally do not learn from watching something on a screen because they are developmentally unable to transfer what is happening on the screen into their three dimensional reality. Children aged 3-5 may benefit from limited use of well-designed TV shows such as Sesame Street and this effect is enhanced if the child and parent watch together and discuss what they are watching. However, many shows and apps which claim to be educational have not been developed in a way which is supported by research and what is known about child development.
Skills which are important for later school success such as persistence, impulse control, emotional regulation, and creative thinking are learned best through unstructured and social play and interactions between a child and parent. So it is much better to get down on the floor and build something with your child out of blocks than watch a video about building something.
Increased use of digital media increases the risk of obesity and the use of media in the evening, especially in a child’s bedroom, decreases the amount of sleep obtained. The data suggests that excessive watching of television in early childhood can lead to delays in a child’s cognitive, language and emotional development. The effects are worse for younger children, more hours watched, and watching things other than PBS (an interesting finding).
When parents spend a lot of time on their phones or watching TV, this decreases the amount of interaction they have with their children which also can have adverse effects on the child.
As tempting as it can be to let the TV, phone, or tablet keep your child occupied, remember that they need to learn to live in the real world, not a virtual world. So play with them, talk to them, and turn them loose to play and explore on their own (in a safe environment). This will help them develop the skills they need in the real world.
Reference: https://pediatrics.aappublications.org/content/138/5/e20162591