Newborn babies that sleep longer, with higher quality sleep, who also have their cognitive abilities heightened would benefit parents and babies both.
tDCS, putting electrodes on the scalp and depolarizing brain neurons with about 2 ma of current, is published as having many effects. Depending on
where the electrodes are placed the user's speed of videogames can be doubled. tDCS is also used to treat depression and raise mathematical ability.
One explanation I read is that the scalp current gradually (15 minutes) depolarizes neurons near the electrode, which is sometimes about 3 cm^2.
Sleep quality and perhaps length can be influenced with tDCS[link]. it is possible that the right locations and waveforms of tDCS could make infants sleep longer, be happier, and possibly learn faster.
So, with lots of safety research: the tDCs baby onesie!
Safety: nonhuman mammals could be given pro-sleep, pro-learning tDCS and then measured as to their cognitive function and social skills as "teen mammals". if the effect on the teens was beneficial or neutral then further studies on humans would commence.
But what about the gooey electrodes?
tDCS depolarization is a gradual 15 minute process, so a new kind of electrode that is dry (conductive carbon fiber) could just sit on the side of the head, perhaps with just 40-60% intermittent contact and still do gradual depolarization. I have not read any research on intermittent electrode function (apparently new) but it seems likely to work.
The onesie would just have some carbon fiber bumpers on the inside of the hood, that mostly worked, most of the time, and could be wiped off.
they could even measure the amount of crying and fussing, and if this makes the babies happier that is a great benefit.