My m#5 is broken in half-there's a huge lump where it's broken. I was told "no walking-weight on it at all"impossible, 3yr old, & a move-the outcome?

NON-UNION. A 5th meta-tarsal (foot) fracture needs immobilization for it to heal or risk a non-union. A non-union is when the bones do not 'grow back together'. The 'bump' may be where the 'bones have shifted'. A bump (or callus) also forms when there is healing. A simple xray will tell what is going on. Podiatrists may prescibe a 'fracture boot' (looks like ski-boot) to wear for 6+weeks. Hang in there!
Okay. Need to know how old the injury is. It is better to put full weight on the foot so the mt head does not heal in a plantar position. If the fx is more proximal it is called a jones fx and could need surgery. It sounds as if you have the fx, not the 3yo.You will probably heal fine.
Depends fx location. Depending on where on the bone the break is located, you may be ok to put weight on it. But you would benefit from a cam walker boot. See an orthopaedic foot and ankle specialist.
Another possiblity. Could be the healing process which made that lump because no cast on it, this condition the bone ends rattle and irritation and big callus could form. I have been in practice for thirty year, I have not seen 3 years old with fracture metatarsal did no heal, but it could happen?