The healthy weight in lbs for a 2 year old boy is 27.5 lbs.
But some 2 year olds may weight a bit more but should not weigh less than 27 lbs and if the 2 year old boy weighs less than 27 lbs then they might be unhealthy and need to gain some weight.
As long as the 2 year old is getting enough milk and enough food to eat then they should keep their healthy weight of at least 27 lbs.
My son when he was 2 weighed 30 lbs and that is healthy as well while my other 2 year old son weighed only 28 lbs.
The weight can be different between different children as some weigh more than others which is normal.
As long as your 2 year old boy is at least 27 lbs they are usually healthy but if you're worried you can speak with your toddlers pediatrician.