this is how I contact a ghost:
sit in a dark room with a piece of paper and a pen
write the letters of the alphabet on the paper and then write what you have to say to the ghost.
Close your eyes and let the ghost enter your body and write their answer.
This works for me so it will most likely work for you
In a room(or where u see the kid more often) Light up a white candle in front of you..And if u like,have cookies in a plate or anythng that you may offer for the kid u want to talk to..
Close your eyes(not really necessary..Just to help u meditate)Then meditate and visualize that the light from the candle is spreading out to every corner of the room..
Visualize as if,there are no furnitures there,just u and the white candle,and the corners of the room..Then,sense every movement in the room,.If you feel his presence already,approach him as you would normally approach,as u said,a kid..But if not,.Call for him,.Say that u just wanna talk,and everythng..But surely,he would be lured by the cookies or watever u may offer,.Keep in mind,that u are dealing with a kid..Kids are more unpredictable,.And playful,.Also,u might wanna n0t have children in the ro0m with you..Better if your alone..Some kids are n0t f0nd with crowds y'know..