This depends on how you teach. If you stress creativity rather than memorization and regurgitation then you should be fine with take home. Of course it can be difficult to come up with problems that require creativity and whose solutions can't just found on the internet.
Just don't put forth rules that can't be enforced and are likely to be ignored. Assume (and make it ok) that students will use all available resources including the internet. Hence the need for creativity. Don't grade on right-wrong but on the basis of intelligent query and response. It may be hard, but possible. Note that even making collaboration improper may be difficult to enforce.
Use peer evaluation.
If you have to assume that students will collaborate no matter what you say, then make it possible to produce joint work. They are a bit young for this, of course, but peer evaluation stresses the positive contributions of the partner, not the "quality". "What was your partner's main contribution." No young person is likely to "rat out" their partner and you don't really want to encourage it. But asking for positive statements avoids this problem. Students doing peer evaluation can/should also do self evaluation: "What was your own chief contribution?"