The 17-year old Jamaican forward will spend time with the Nerazzurri's Primavera academy squad until DC's preseason opens in a fortnight.
A United spokesman told MLSsoccer.com: "I spoke with him today when he got to Milan.
"He's really excited about this opportunity and will train with Inter's Primavera team ... for two weeks before joining us in preseason. This is our first exchange since the official partnership with Milan, and we hope it is the first of many."
Jamaica international Seaton joined DC's senior roster as a Homegrown Player in January 2013 and spent most of last season on loan with USDL Pro affiliate Richmond Kickers.
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