I have checked several language learning apps for android.
With lingling there is a strange thing that it randomly offers very rarely used words. Words which are used by adults and not by 3 year olds.
The only app we found useful is MyKoala. It does not have that advanced teaching part - but it starts with easy words like animals and fruits. And, the most important, with one download you get dictionaries of very many languages, and even rare languages (like my language) are included. So my 5 year old get answers in her native language; other apps do not offer this.
I was surprised that she checked right most of the answers; I do not teach her English directly and I did not know that she can read English