This is just a quick round-up of tyres in the 20" x 1 3/8 size (451mm ERD) that may be suitable for kid's use for offroad riding (not BMX track racing).
- Intense MK2 - low rolling resistance, light weight (250g) but probably not enough grip for offroad riding;
- Schwalbe Mow Joe - good grip, reasonable light weight (330g), may work tubeless ( 24" versions certainly do ), but much more expensive that other tyres;
- Kenda Small Block 8 - lots of little knobs, light weight (280g +/- 15g claimed), may be a good rear tyre option;
- Maxxis Holy Roller - has worked well as a rear tyre. Cheap and widely available. Weight unknown;
- Tioga Competition III - lightweight at 300g - has worked well as a front tyre offroad. 25th anniversary version has lower profile knobs that are closer together and probably would not be as good on the trails (more of a BMX track tyre);
- Tioga comp X - 310g in wire bead, looks to have a good chunky knob pattern;