The units will try to authenticate to wireless but end up failing, with a error code that says to check settings.
Nintendo implemented wifi authentication in a way that relies on outdated technologies. While the devices support 802.11b/g(/n), they require 802.11b to make the authentication handshake. Strangely enough, the older DSi units do not rely upon the slower protocol and will connect to our network with no problems. UMD has had 802.11b disabled since late 2011, for enhanced network performance.
Use another device as a hotspot, or a usb to ethernet adapter.
What else can you do:
Contact Nintendo and ask them to rewrite their wireless authentication to only use g or n.
Additional links for information:
Rev: 8.14 alj