Bloated kind of tummy is common in toddler due to the curve of the spine around that age. Toddlers are children aged 1 to 3 year. However also make sure that the child is not constipated.... Ensure that they eat fruit and vegetables and move the bowel regularly. Also deworm them regularly. Some children could have also abdominal organs enlargement. However such children are usually sick as well. So if your otherwise healthy toddler has what looks like big tummy... But not hard, no vomiting, no diarrhoea, no constipation.... Then DON'T WORRY ABOUT IT.
However any SICK child with bloated tummy should be seen by a doctor preferably a Paediatrician or Paediatric Surgeons for thorough evaluation.