And whence is it derived that minors (who were killed by a tam) are equated with adults? It follows, viz.: Since a tam is to be stoned and a mued is to be stoned, if you have learned about mued that minors are to be equated with adults (viz. 21:31), then there (re a tam), too, minors are to be equated with adults.
The Shared Punishment Stoning Creates a Shared Scope Minors Included
Mekhilta Tractate Nezikin 10:5