First off, it probably doesn't matter whether or not you're selling the actual toys or just the designs - it's the designs that are protected after all, in whatever form they may end up appearing. That being said, people do this all the time, even in the US. It's usually not legal, especially if sold for profit (rather than, say, given away as a prize or whatever). If they decided to take legal action, you'd likely have to forfeit all proceeds plus pay penalties.
As long as the operation is very small, they're unlikely to come after you. But that's never a guarantee, since there's often a "use it or lose it" situation in copyright that forces them to protect their IP or be at risk of forfeiting the copyright. Cease and desist letters from lawyers are not uncommon.
The safest way would be to just not do this. You can try skirting the fringes with deniable designs (as suggested above) but that's by no means a surefire way of avoiding legal trouble. If they want to go after you for it, they can; and they'll win. Heck this thread could well turn into "Exhibit A" during a trial, demonstrating you knew this was potentially illegal
It's probably not worth the risk, considering even a small legal problem can balloon into epic costs in many legal systems (especially the US). Even without a trial, just engaging a lawyer to communicate with them can easily ruin your day.
[this is not legal advice, just friendly advice]