Your son is very active. But he speaks less. That is his nature. The reason is lagna (self) and 3rd (Right ear) sub lord is Mercury conjoined with Sun in an airy sign. When lagna is connected with Sun, those natives like to be isolated and do not move freely with others. They speak less.
Another factor 2nd sub lord Venus is watery sign conjoined with lagna lord Saturn and is in the star of Mercury in an airy sign. So the native does not like to speak freely with others. But as Venus is connected with airy sign, he will definitely speak well. Jupiter is lord of 2nd house and aspecting it. But Jupiter and 6th lord Moon are in the 8th house . So there would be some speech problem and delay would be there. Mercury and Sun are aspecting 3rd house. So please check up his hearing capacity also.
The running period is of Moon dasa-Venus bhukti upto 03-07-2022. Next bhukti is of Sun which is upto 01-01-2023. There would be slow improvement in speech also.
Cure : Mars is good in 11th house and aspecting 5th house. Mars period starts from 01-01-2023. So You will be happy with your son in this period.
Due to Jupiter’s impact, he will get better and will be able to speak but problem will always be there. Some kind of speech related problem should be there through out life even if he speaks, it will not be proper or clear. It is also indicated that his parents will suffer mentally and financially on account of him.
So, I feel you can hope for betterment to certain extent but not cure.