Well, it's written in Chinese pinyin. If you're a beginner, it's a bit confusing. ta(1 ) could refer to both male and female when it's written in pinyin. Although, if it was in the character form 他or 她 it wouldn't be so ambiguous. Tā xiǎo de shíhou bù rènshi tā. The meaning of this sentence can be either way as follow " when he/she was young, didn't know him/ her". I hope this helps a little. Good luck.

Yes it makes sense. When are you going to get Chinese input? 他小时候不认识她。 He didn't know her when he was little. 她小时候不认识他。 She didn't know him when when she was little. Or any combination thereof.