Hi,
fellow psych student (well, actually graduate since about a month - huzzah) here. You mentioned that your "new" lab is in developmental psych. From personal experience I can (unfortunately) tell you that working in developmental / cognitive psych lab "on the side" will not be as beneficial as you might hope it is (unless this is the research you would like to do for your PhD).
I am assuming your developmental lab is as most labs of this type, and so the research done there is taking little kids, giving them a behavioral task and then code the data (please correct me if I am wrong). The problem with this, though, is that running these tasks / experiments takes quite a bit of time (you have no idea how few participants actually bother to show up on time), you have to do it with quite a few participants and you will overall invest a looot of time into this (participants are scheduled in mornnings or afternoons, which will either conflict with your class time or your time in the other lab) , while most likely not learnig any techniques that will be beneficial to you when you do your PhD (exception: if you do a psych PhD) or that will impress your future PI or interviewers. On the other hand, the increased time you put into developmental psych is probably going to affect the time you put into the neurobiology lab (and thus your performance there) - your PI there will most likely not be amused. So the danger is that you'll end up doing mediocre work in two labs as opposed to splendid work in one lab, and thus get two mediocre LORs as compared to one amazing LOR.
Thus the danger is that the payoff might be significantly lower than the costs.
Of course there is the chance that you could still excel in both labs and in your courses (and if you do congrats, more power to you 🙂 ), but the danger of decreases in performance is imminent and should not be underestimated. I am currently trying to handle this balance act (working > full-time in one lab, while working part-time/nights in another lab because the supervisor doesn't wanna let me go), and while my work at the full-time job is not suffering, my work at the part-time lab is doing so significantly ( p < .05)
Sorry for the pessimistic post 🙁