If I was sitting up a trailer for a child I'd have some good red blinkie's ( 50+ lumen ea. ) on the rear and a couple 70 lumen white strobes aimed out to the sides. Used with good daytime yellow or orange on the trailer I'd also slather on the reflective tape. Just make sure no strobes or bright lights are aimed at your kid.
All this said, would I take my toddler out for a ride on the traffic packed roads of my local area?...Not in a million years.