Bal Gopal Mantra
The "Bal Gopal Mantra is available at page No.16 of India's "Geeta Press Gorakhpur's Publication, namely "SantanGopal Strotra" book costing Rs.4/- only.
You can get the same from them by checking from their website and email id given
firstname.lastname@example.org & web site
"Om Shreem Hreem Kleem Glaum Devakisut Govinda Vasudev Jagatpate Dehi Me Tanayam Krishn twamaham Sharanam Gatah"