As the others have said, Namlan, "keep pleasing" isn't really appropriate. Your son could be pleased that you're home from work early or he could be pleased that you spent an hour with him playing in the backyard. The context of your sentence really has nothing to do with him being "pleased" and everything to do with him being "spoiled" or "over-indulged".
Just for argument's sake, let's replace "please" with "spoil". In that case, the original sentences would be:
"If you keep spoiling your son, he will be very naughty"
"If you continue to spoil your son, he will be very naughty"
"Keep spoiling" would probably be more commonly used but either sentence is perfectly correct and natural.