There is more to the question than first seems. The answer depends on the nature of the relationship.
For long-term exclusive couples it is entirely up to them and communication will be established.
For first time meets or casual encounters sex is never included unless explicitly discussed and agreed (and even then without compulsion on the day). Nobody should ever assume or jump to the conclusion that a suckling meet includes sexual activity. The two things may be closely linked in terms of both being methods of interpersonal bonding or expressions of a type of intimacy, but they are entirely separate in terms of consent.