Unfortunately, you also have to keep in mind of the laws and ages of the people participating in said giveaway, not just your own. There's a reason why even in giveaways advertised online or on TV they have that fine print that clearly states laws. For example, the dubbing contest SE is holding now limits who can enter (including who can even help make the video/audio) by country precisely to avoid specific issues. While it's not a giveaway, they're still giving up items with monetary value in return for something. In giveaways the participants are still entering, which is what they give in return for a chance at the goods you're offering. For some weird reason, a lot of countries have huge rules regulating that.

It's really stupid, and it's a killjoy, but it really is better to be safe than sorry. Depending on who's participating in your giveaway I think the previous suggestions of giving hard to obtain in-game items instead would be safer.