I think there are some usual misconceptions that keep repeating over time. First of all: adults can send messages to children at Vikidia. They can't send private messages and you can't send private messages at Wikipedia if you don't fill down the e-mail option. Children below 13 years old CAN'T legally have an e-mail, so they souldn't fill this section wherever they are creating an account. Larger communities may have different problems, but actually you don't ask for age when creating an account, so you may have underage contributors now at ptwiki. I assume there are underage contributors there, as we don't ask for age.
Second: children are reverted at Vikidia. I can easily find content reverts there. If Vikidia users are not reverting, editing or discussing with other users, then the content may be compromised easily. There's vandalism at Vikidia, too. You have the same social issues at Vikidia that exist at any given Wiki. But Wikipedia has a larger community, so it is easier to find solutions, even technical solutions (ORES, filters...) that are not available at Vikidia.
Third: children and young editors are currently writing at Txikipedia on topics that adults are not covering. And they are doing it great. This is a really weak argument, as we do have articles that are only at Txikipedia, and the community is really happy about it. Why should it be different at any other given Wiki?
Fourth: As a fact, we received exactly the same comments when we created Txikipedia, and reality has proven that we were right (700 articles in 5 years at Vikidia vs 2000 at Txikipedia in 2 years) and that this can be done. Teachers are delighted, we are having more events at schools than ever, and children are writing about their hometown, about the topics they like or creating biographies in a rate we haven't seen before. In a month we will have more new articles that were created at Vikidia in any given year. So, we can also create education resources INSIDE Txikipedia and use it at schools.
I hope Portuguese community finds the way best fits their needs, but I would appreciate to be honest about our claims.