Use pineapples, coconuts, guava, or mango (oh heck, you can use oranges if you get desperate... we're going for fun here, not authenticity... just write PINEAPPLE on your orange with a black marker *grin*).  You can use real fruit or plastic fruit (or make bean bag fruit out of pieces of felt).

The age groups can compete with each other (mommy and daddy can compete with their 2 yr old), just make each does the activity appropriate for their age to even things a bit (though the 2 yr old may just stop and stare in amazement when they see how goofy mommy and daddy look).

AGE 5+ Basically team members have to run to the end, holding the pineapple between them (without hands) ... stomach to stomach or hip to hip. If they drop it, you can allow hands to be used to reposition it. If you find the pineapple too heavy for the kids, use a mango, papaya or guava instead.

AGE 3-4:  Same idea, but don't team the kids up.   Let each carry their own fruit, but in an odd way ... between their knees (hard), behind their back (medium), with one hand (easy).  Younger, less athletic kids should get an easier way of carrying.

AGE walking to 3:  Just let the youngest ones get to the end carrying their fruit.  You'd be amazed how tough it is for them to concentrate on running and carrying simultaneously.