Substantial research suggests that high variability (multitalker) phonetic training helps second language (L2) adults improve differentiation of challenging nonnative speech sounds. Is such training also useful for L2 children? Existing studies have mixed findings and important limitations. We investigate the potential benefits of computerized phonetic training for 50 Dutch 7-year-olds and 39 11-year-olds trained on English vowel contrasts in a 2-week study in a classroom setting. Half received multitalker, and half received single-talker input (i.e., high variability vs. low variability; HV vs. LV), with learning evaluated by a battery of tests. Both groups improved in training; however, 11-year-olds improved more. Moreover, 11-year-olds showed generalization to novel talkers, and 7-year-olds did not, with Bayes factor analyses providing evidence for the null. Generalisation in 11-year-olds was no greater following HV than LV input, with evidence for the null on one of two tasks where generalization was found. Results are discussed in terms of the interplay between age, task demands, and talker variability.