What are the options to replace the lost tooth in case a child 2.5 yrs of age lost his upper front tooth (milk tooth) along with roots?

Since the child is 2.5 years of age, it would take about 5.5 years for the permanent counterpart(central incisors) to erupt. The upper (maxillary) central incisors generally tend to erupt at around 7–8 years.

Since the child has lost his primary incisors so young, it's gonna be a must to maintain that space. When primary teeth are lost earlier that necessary; the adjacent teeth tend to migrate into that space and thereby causing loss of the arch space. This leads to lack of space for the succedaneous tooth to erupt. In this case that would be the central incisors and eventually ending up with malocclusion. There are however studies which say that when teeth anterior to the canines are lost after the primary canines erupt; there isn't a loss of space and the arch remains stable