I think it's actually a much greater value proposition for someone with no status. If OP's family is planning to check a bag for each person, then the potential cost of checking bags can be 'deducted' from the upgrade expense. As FC pax, the checked bags will also get United's coveted VIP tag.
Intangibles:
• OP and family an board early and settle in. This will relieve some of the stress of traveling with little ones.
• OP and family may get better IRROPS protection given that a portion of their itinerary is in F.
• Innumerable 1Ks will be ticked off seeing a family of 4 "kettles" (esp. 2 kids) seated in FC when their upgrades fail to clear. (We'll hear about it on FT.)