I wish we could tag our answers to be found easily in the future. Here is my answer to a similar question from last week. I hope it helps.
We've been through this, but not at 7 years old. A bit older. However, I think that we handled it very well.
We found inappropriate content on my oldest son's iPod. We were surprised, and our initial reaction was to put him on restriction from all devices to punish him. But after my husband and I thought about it for awhile, we determined that restriction and locking his devices down even more would not teach him to navigate the world more effectively. So we took a different tack.
We discussed with the kids why it's not appropriate for kids to be looking at that sort of adult stuff. Heck, it's not appropriate for adults. Of course, we broke this down in age-appropriate terms. We talked about intimacy and how that it is supposed to be special, between two people who love one another, such as a husband and wife; and how the internet has perverted intimacy to the point that it causes problems in marriages and relationships. We want our kids to grow up with healthy ideas about intimate relationships, and we explained that stuff like that is not what healthy relationships are all about. Also, all of those naked people are someone's son, daughter, sister, brother... and some are victims of human trafficking and don't want their pictures on the internet. Every time someone searches and clicks, they are contributing to human trafficking. We don't want to be the kind of people who do that. We still have ongoing conversations about guarding our hearts and minds from evil and inappropriate things, and why.
And then, after we discussed at length, and answered their questions, and deleted their browser history...we handed their devices back. We said, "Now that you know, I think that you will choose better." And they have. We still check their browser history, we still block explicit content. But you and I both know that even the "safe" browsers can't block everything. Still, we haven't had a problem since, and the kids have learned a valuable lesson about self worth, intimacy, and the worth of other people.