Hi - sorry you have been ignored so far, and I thought I should take pity on you!
I am a retired TA (male) and worked with primary age children for twenty years.
Obviously 'concentration' is not something one can teach or enforce, and possibly the life-style in other countries may be different from the UK, which may result in young children behaving differently.
When our son was little (30 years ago) he had both parents at home most of the time, so received a lot of attention, playing-with, conversation etc. Also, unlike many households we never had the TV or radio on, except when we were actually watching/listening. Although I have not heard this proposed elsewhere, I have always considered that the constant background of TV/radio does not benefit children. We live in the country and when DS was in his pushchair we often walked near a little stream; he would watch the flowing water, and we would stay as long as he wanted to, maybe 10 or 15 minutes or more.
Music and TV were things he enjoyed as a treat, and even before he could talk he would point to the tape recorder and go "Ooo-ic, ooo-ic" (music) and we had several tapes of pre-school songs recorded in nurseries, that he loved. We played with Duplo and Lego with him, read to him, and let him watch limited amounts of appropriate TV ( Thomas the Tank Engine, Rainbow, Pob in those days.) But he might also see a BBC classic serial, or a Prom concert occasionally.
All these things, I think, allowed him to develop great concentration, with the result he did well at school, university and now has a good career.
Children need to be stimulated, but over-stimulation is probably bad thing. So I would suggest :
Have a quiet, relaxed atmosphere at home;
Play and talk with the child as much as possible;
Have toys and games that encourage play for extended periods of time, eg Lego, and work with child following instruction leaflet;
Do craft activities - cutting out & sticking; drawing & painting; simple sewing, tapestry, even knitting is possible for 5 or 6 year olds.
Look at nature - birds, animals, insects, or do gardening activities;
Share music (NOT Pop) and appropriate TV with the child, talking about it afterwards;
Share appropriate computer activities with child, and talk about it. (Our DS was writing simple computer programs at age 6, on a primitive computer, but modern computers do not facilitate that, except for the £25 www.raspberrypi.org/about );
Engage in imaginative play - dressing up, dolls' tea party, puppets.
I hope this is of some use to your friend, and if I can be of any more help let me know via a PM if you wish.
Cheers