One visable now ?
It is common for infants & toddlers to have loose belly muscles and a ridgelike outpouching may be visable in the middle from the breastbone to the naval+.
These muscles need to be loose in pregnancy
if nutrients are to move thru the placenta
to the inside.As babies get more mobile & start doing "crunches" thru normal activity the muscles tighten & the ridge disappears. If not, it can be fixed >4y.