The original version of this article was published containing errors misreporting word token and type counts and the statistical values associated with these counts. These errors and their corrections are detailed below. The corrections do not affect the nature of the results or the basic conclusions of the article.

(1) Error: An error was found in the second half of the following sentence on p. 953, under participants: “The two groups of children that form our sample were thus comparable in their productive spoken vocabulary for word tokens (M_TD = 168.26 [SD = 125.18] vs. M_DS = 145.43, [SD = 88.75]; Kruskal–Wallis, H(1) = .21 p = .64) and were marginally different for word types (M_TD = 28.43 [SD = 26.90] vs. M_DS = 18.34, [SD = 22.78]; Kruskal–Wallis, H(1) = .3.83 p = .05) at the initial observation.”

Correction: The corrected sentence should be as follows: “The two groups of children that form our sample were thus comparable in their productive spoken vocabulary for word tokens [M_TD = 51.91 [SD = 59.68] vs. M_DS = 25.26 (SD = 39.39); Kruskal–Wallis, χ ² (2) = 3.53, p = .06], but were significantly different for word types [M_TD = 18.48 (SD = 20.51) vs. M_DS = 11.22, (SD = 18.87); χ ² (2) = 4.37, p = .04] at the initial observation.”

(2) Error: An error was found at the end of the first paragraph on p. 959: “In fact, children with DS who did produce baby signs in our study also had larger repertoire of spoken words at their disposal than the ones who did not produce any baby signs in the initial observation session (M = 24.21 [27.55] vs. M = 9.2 [6.28], H(1) = 6.22, p = .01). Moreover, when we estimated children's vocabulary size (i.e., number of different referents conveyed) using both speech and baby signs in the initial observation, the extent of children's vocabulary became comparable in the two groups (M_DS = 20.52 [SD = 23.71] vs. M_TD = 28.43 [SD = 26.90], H(1) = 2.01, p = 0.16).

Correction: The corrected sentence should be as follows: “In fact, children with DS who did produce baby signs in our study also had larger repertoire of spoken words at their disposal than the ones who did not produce any baby signs in the initial observation session (M = 16.0 [22.96] vs. M = 3.78 [4.44], H(1) = 6.57, p = .01). Moreover, when we estimated children's vocabulary size (i.e., number of different referents conveyed) using both speech and baby signs in the initial observation, the extent of children's vocabulary became comparable in the two groups (M_DS = 13.39 [SD = 19.86] vs. M_TD = 18.48 [SD = 20.51], H(1) = 1.77, p = 0.18).