I went through this with my son as a 12U and a 13U this year. My son is a righty and is a pitcher/3B type. 5'10" and 140 lbs as a 13 year old. He started hitting lefty because all of the kids in our neighborhood are 2 years younger and they wanted to make it even so he taught himself to hit lefty with a wiffle ball bat. In 12U the travel coaches let him hit lefty or righty whenever he wanted so he mixed it up and had pretty equal results. That changed this 13U year as he hit 2X higher BA as a right handed hitter than he did a lefty though he had good power from both sides. Ultimately the coach told him to switch to righty only as he a pretty good pitcher right now and that is where they see him. Sounds good but we are going to keep hitting on the side lefty and in local rec league as lefty exclusively to keep the swing.
My biggest advice is switch hitting is 2X as much work - if everyone else is hitting 3 times a week with their regular swing, your player needs to hit 6 times.