Is it normal for infants & toddlers to have greenish stool first after diarhea that turns into yellowish later on i.e it is a part of recovery.

Yes, expected: It takes time till the gut regains its normal function, hence the different stools colors, so long the child is otherwise healthy

Pretty common: The greenish color in stool is the breakdown product of the bile when it has not been in the gut long enough to go through a change to yellowish or brown. It is normal as is the loose consistency. Some digested material will take on a darker tint than others & the germs in the gut will also impact the final product. I'd ignore the whole issue.