Hi my 18 month old grandson has an increasing amount of water filled bumps. Landon does not have any known allergies, nor does he have any obvious illnesses now. He is teething, though. The bumps are all over his legs, arms and tummy. He hasnt been

Hard . Hard to tell without a picture, but perhaps he has either eczema or molluscum contagiosum. Take a look at the picture below to see if it looks similar to molluscum. If so, i would visit a dermatologist to confirm the diagnosis and discuss treatment options. I hope that helps.
Chicken pox. Water filled bumps sound like chicken pox until proven otherwise.
Not teething . Teething does not cause fluid filled bumps on the legs, arms, and tummy. Something else is going on here. Since he is only 18 months old you really don't know if he has any skin allergies or not. He hasn't been exposed to that many things yet. I think he needs to be seen by his pediatrian to figure out what is really going on.