Advantages in teaching the two hand forehand are many for juniors and even adults.  The negatives are minimal.  There will be many opportunities to convert to a single hand forehand as the player develops.

The main advantage of the two hand forehand is its simplicity and mechanical similarities to the modern forehand.  There a many, many disadvantages to teaching single hand forehand including the litany of bad habits that typically form in the early development…taking the racquet back too far, not turning shoulders during the preparation phase, losing the synchronization of the unit turn and the forward path of the elbow, using the wrist too much to accommodate for timing issues.  Early two hand instruction promotes a good shoulder turn while limiting the racquet take back which improves contact timing and consistency. Using two hands can also speed up the racquet size promotion, which is important as the lever length increases, the stroke will change slightly and the sooner kids can advance to a 27″ racquet the better it will match the stroke mechanics.   Over time, as the player develops you can start taking one hand off just before contact and then eventually start exclusively training one handed if this is the preferred pathway. For some, they may decide to stay and play two handed which would not limit any upside development as there have been many D1 college players that play two handed off both sides.

My coaching progression approach starts with a hand rally, then a push rally where you place the hand behind the strings and push the ball to the target, then we progress to two hands on the handle: https://tennisdevelopmentinnovation.wordpress.com/2022/05/24/home-tennis-training/

There are a few variations of the two hand forehand and here is Ilija Bozoljac with the dominant hand high version:

https://youtube.com/clip/UgkxvP_etkfuPGZz0jEFZwCohmeLbcJokUQZ

https://youtube.com/clip/UgkxvP_etkfuPGZz0jEFZwCohmeLbcJokUQZ

The alternative method is to not switch hands and keep the dominant hand low like

Peng Shuai

Playing with two handled racquets

These two handled racquets really help develop modern mechanics and better unit turns and more coordination of the torso into the shot. The two handled racquet can help players become more proficient in tennis sooner than traditional one handled racquets.

JT Nishimura  https://youtu.be/jzGgViwg7Mo?t=19m2s