You can give arhar as well as moong daal water..as he is having Loose motions some suggestions are...rice water means after you boil rice strain it for its water..give with a pinch of kala namak..that helps..also boil Apple and give its puree...

You can give dal ka pani ..or little dal too.. the stomach takes time to settle si the lighter the better . Tc

Give him a little curd mixed in the daal. Also give banana. It is binding