Recently, I have contacted a psychologist, learning & development specialist regarding this issue and he told me that most of the kids are facing the same issue nowadays after that he suggested me some tips and those tips I would like to share with you:- serve them healthy & greens food, fix a routine to follow, set up a compensation method, play focus games, get your child’s way of learning, naps boost concentration and activities to build awareness.
Don't worry too much if he is not concentrating on his work right now. But if you want then you need to do a few efforts. First, you can buy such toys that attract him and little bit complex just like puzzles or cars that will grab his attention and he will play with it instead of coloring books, or you can buy such coloring books that have pictures like car, apple or other things, so while coloring he learn about the things. If your son is not responding to others then go to your friend's house who have kids of the same age and let them play. After a few minutes, only you can see that your son start playing with them. It is normal behavior of kid to play with others all he needs is a friend with whom he can play that's it. This will work.