Your team talk after the loss was very important for that.
Young players are much more moody, so if you've got a team full of wonderkids its no wonder. Veterans with high professionalism, determination, work rate, etc, are much less likely to be so impacted.
You have to keep their spirits high. If you're on a good winning streak and you finally give one up, you gotta keep your team up high to get back on track.
I think morale has the correct level of effect but the issue which may be in existence is how much it fluctuates in a short period of time. Your right in saying that one or 2 defeats in a row should not cause morale to hit rock bottom no matter what team talk is used