I was pleased to have the opportunity to review this work. The study addresses a relevant topic and it is a valuable addition to the scientific literature. However, it has some limitations that should be addressed.
Major comments:
1. If I am not wrong this study was performed in a 5-month sample (around 150 days). However, according to table 2, samples significantly (p<0.001) differ in age. One of the samples (twin sample) is more than 20 days younger than the other sample. I appreciate that age was included as a covariate but I believe that this could potentially impact the results. A sensitivity analysis could be performed adjusting the samples to be comparable.
2. Looking at table 2 it seems that there are a lot of extreme values. In my opinion, analyses should be performed removing outliers since this could potentially influence the results as well (could be added as a supplement).
3. My major concern is about how some variables such as breastfeeding could explain these results. There are no differences between singletons and twins in most of the variables of this study but there are when it comes to wake ups. However, this is very likely explained by breastfeeding and co-sleeping practices. It is well known that breastfeeding and co-sleeping are associated with more wake ups (also with longer sleep duration) and it is also well known that twins are less likely to receive breastfeeding. This is a potential confounder and should be addressed (at least discussed and acknowledged as a limitation).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6464508/#CD012003-bbs2-0046
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1201416/
https://pubmed.ncbi.nlm.nih.gov/34582549/

Minor comment
1. I appreciate just one of the singleton samples is also longitudinal but if several time points are available for both samples, the authors may want to strengthen this paper by adding more time points analyses (e.g. at 2mo).

Thank you so much for the opportunity to review this paper again.

The authors have addressed all my comments. I think the paper is stronger now and it is ready for publication.