How to share common code across analyses in R - r

Question

I’ve copied codes into parent and child file and located the child as C:/temp/child.Rmd
The statements in parent program
---
title: "parent"
output: pdf_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
library(dplyr)
library(ggplot2)
```
```{r, parent, include = FALSE}
src <- lapply(
sort(unique(iris$Species)),
FUN = function(x) {
knitr::knit_expand(
file = here::here("C:/temp/child.Rmd"),
title = x
)
}
)
```
`r knitr::knit(text = unlist(src))`
The statements in child program
---
title: "child1"
output: pdf_document
---
## {{title}}
```{r plot_{{title}}}
iris %>%
filter(Species == "{{title}}") %>%
ggplot() +
aes(x = Sepal.Length, y = Sepal.Width) +
geom_point() +
labs(title = "{{title}}")
```
When I knit the parent program, the error message as below. Why and how to fix it?
Quitting from lines 14-23 (trypc.Rmd)
Error in file(con, "r") : cannot open the connection
Calls: <Anonymous> ... one_string -> paste -> read_utf8 -> readLines -> file
Execution halted
Thanks