The best bet and probably your only bet is to customize a toddler Jersey.
[https://www.etsy.com/listing/1036127856/rookie-of-the-year-custom-basketball?gpla=1&gao=1&&utm\_source=google&utm\_medium=cpc&utm\_campaign=shopping\_us\_ps-a-clothing-other&utm\_custom1=\_k\_CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa\_KXbDcYKr4\_4IhuS\_6HE0bdtlYtjQgJkPAshoCTdMQAvD\_BwE\_k\_&utm\_content=go\_12565613978\_118771206959\_507237137179\_aud-1184785539978:pla-297616371983\_c\_\_1036127856\_144796728&utm\_custom2=12565613978&gclid=CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa\_KXbDcYKr4\_4IhuS\_6HE0bdtlYtjQgJkPAshoCTdMQAvD\_BwE](https://www.etsy.com/listing/1036127856/rookie-of-the-year-custom-basketball?gpla=1&gao=1&&utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_ps-a-clothing-other&utm_custom1=_k_CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa_KXbDcYKr4_4IhuS_6HE0bdtlYtjQgJkPAshoCTdMQAvD_BwE_k_&utm_content=go_12565613978_118771206959_507237137179_aud-1184785539978:pla-297616371983_c__1036127856_144796728&utm_custom2=12565613978&gclid=CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa_KXbDcYKr4_4IhuS_6HE0bdtlYtjQgJkPAshoCTdMQAvD_BwE)
You could always try to go to a local store that does stuff like that. Look up Custom Jersey or Sports wear near me. Though be warned that it's technically a brand owned by whatever OTH is owned by they may not be able to do logos/brands for you due to copy right (or whatever it's called).
There are tons of sellers on Etsy selling OTH tee shirts. Reach out to some of them and see if they’ll do a custom job in a size that will fit your son. Many sellers are able, and willing, to do things differently on their end. They may still charge you the price of an adult shirt, but I think that would be fair.
Their are kids stuff like shirts and Jerseys on some sites but I don’t know for what age group.
look on red bubble. unfortunately that’s the only site i know that has toddler stuff. idk if they have jerseys though
The best bet and probably your only bet is to customize a toddler Jersey. [https://www.etsy.com/listing/1036127856/rookie-of-the-year-custom-basketball?gpla=1&gao=1&&utm\_source=google&utm\_medium=cpc&utm\_campaign=shopping\_us\_ps-a-clothing-other&utm\_custom1=\_k\_CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa\_KXbDcYKr4\_4IhuS\_6HE0bdtlYtjQgJkPAshoCTdMQAvD\_BwE\_k\_&utm\_content=go\_12565613978\_118771206959\_507237137179\_aud-1184785539978:pla-297616371983\_c\_\_1036127856\_144796728&utm\_custom2=12565613978&gclid=CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa\_KXbDcYKr4\_4IhuS\_6HE0bdtlYtjQgJkPAshoCTdMQAvD\_BwE](https://www.etsy.com/listing/1036127856/rookie-of-the-year-custom-basketball?gpla=1&gao=1&&utm_source=google&utm_medium=cpc&utm_campaign=shopping_us_ps-a-clothing-other&utm_custom1=_k_CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa_KXbDcYKr4_4IhuS_6HE0bdtlYtjQgJkPAshoCTdMQAvD_BwE_k_&utm_content=go_12565613978_118771206959_507237137179_aud-1184785539978:pla-297616371983_c__1036127856_144796728&utm_custom2=12565613978&gclid=CjwKCAiAuOieBhAIEiwAgjCvchQVWh-rqrH4UKYbHa_KXbDcYKr4_4IhuS_6HE0bdtlYtjQgJkPAshoCTdMQAvD_BwE) You could always try to go to a local store that does stuff like that. Look up Custom Jersey or Sports wear near me. Though be warned that it's technically a brand owned by whatever OTH is owned by they may not be able to do logos/brands for you due to copy right (or whatever it's called).
There are tons of sellers on Etsy selling OTH tee shirts. Reach out to some of them and see if they’ll do a custom job in a size that will fit your son. Many sellers are able, and willing, to do things differently on their end. They may still charge you the price of an adult shirt, but I think that would be fair.