Or HaChaim on Numbers 7:5/אור החיים על במדבר ז׳:ה׳

1 קח מאתם, "accept it from them!" The reason the Torah wrote the word מאתם (instead of מהם) is that as of that moment the gifts were still the property of the princes and had not as yet been transferred to Moses. The reason that Moses had not as yet accepted the gifts was that he had not been commanded that the Tabernacle be transported on wagons and did not know what else to do with them. The princes had reasoned that seeing the boards and the sockets of the Tabernacle were large and heavy respectively, they would need to be transported on wagons. As it turned out, G'd agreed with their reasoning.