It’s a common practice, a problem with authentic child actors is they generally change once the original actor hits puberty, so higher pitched adult voices are common.

One of the behind-the-scenes videos on a Ed Edd n Eddy disc had some funny stories of the voice actors meeting fans (e.g. Ed’s VA spotting some kid watching the show on a TV while on vacation in Jamaica and throwing in a “huh huah, thut guy is funneh…”) and Kevin’s VA had to keep doing their voice since kids didn’t believe her whenever she mentioned it.