A trailer is my most useful accessory, should have got one years ago.
Use a child-trailer for children. If you want to haul stuff, get a cargo version.
For touring, use single wheel (better tracking), for utility, 2 wheels: (heavier loads, long loads)

I prefer a flat-bed style, I can add any kind of box or use the flat bed for sacks of DIY supplies and lumber.

Recently, I had to move some gravel around. I took my tools in a plastic box and used the box as a wheel-barrow.

I fretted between the small 16" wheel and large 20" wheel. the large one has been a good choice. It disassembles with ease for flat storage.
I only use the trailer when I intend to haul stuff.