It's possible that you're overdressing them for bed. Remember the rule of thumb: only one extra layer than you feel comfortable in. Over-bundling your baby can lead to overheating, which can cause heat rash. If you can, purchase breathable, organic cotton clothing. A cotton sleep sack that is a wearable blanket is a great option in the winter or cooler nights. Babies can also wear beanies to keep their heads warm. Avoid blankets or any loose clothing that can cause a risk for suffocation.