My friend has made app for montessori kids, But I am not sure whether I should allow kids to learn through app. What I found is kids love gadgets. Its hard to keep them away from mobile and say no. So I thought of letting them play this learning game instead of wasting time on some other games. What are the thoughts of experts on this?

Everyone's an expert on this site. You can be one too after a while!
Yes, kids love gadgets. You don't say how old they are. My theory is to let them play the learning game (and some minutes for some others) for a fixed amount of time each day, as long as they play outdoors a more flexible amount of time too, depending on the weather. You decide how much. Rules aren't as important as love and consistency.

My friend has made app for montessori kids, But I am not sure whether I should allow kids to learn through app. What I found is kids love gadgets. Its hard to keep them away from mobile and say no. So I thought of letting them play this learning game instead of wasting time on some other games. What are the thoughts of experts on this?

My son has little interest in iPads right now, 16mo at the moment, but my daughter loves my iPad and her LeapPad, she just turned 3.

She doesn't play on my iPad all the time but does so for a few hours through out the day. I have read conflicting studies about whether screen time is good for kids or not. Since this is so new there isn't a good pool of papers to form a general consensus. The majority says to limit screen time, but there are a few that say that it doesn't matter.

My daughter picks up on the nuances of apps quickly, and knows which ones are hers and which ones aren't. She navigates around the iPad quite easily. I do worry at times if we let her use it too much, but we want our kids to know and be comfortable with technology as they grow.

Honestly it is up to you and what you want for your kids.

There are a lot of studies out regarding brain development and screen time. As a teacher, I've noticed a steady decline in the ability to capture a student's attention because I do not move at the speed of a tablet or video game. Less than an hour of screen time per day for a 4 or 5 year old is appropriate. Just remember that if your child can't sit and listen as you read a "real" book, or can't put together a puzzle, I'd limit the screen time even more. Attention skills are necessary for learning. Work on that so your children can be good students in the classroom.