I have used some mineral oil on the ebony fretboard of guitars but that was years ago. My luthier is opposed to oiling fretboards and he says that it clogs the pores of the wood which degrades quality and makes cleaning difficult. I am not sure if I agree with him but he certainly knows a lot more about instruments than me.
Based on what I casually read on the Internet... I think lemon oil is mineral oil with lemon scent added; and, since baby oil is also mineral oil with added fresh scent, baby oil should work just fine on your fretboard. (Also, you don't need to oil a finish maple fretboard, just in case your uke has one; unlikely.)
There is the generic Lemon Oil and there is real Lemon Oil.
Generic Lemon Oil has a lemon scent added to a concoction. I would not even use it on furniture.
Real Lemon Oil is made out 100% lemons, the lemons are processed to harvest the actual oil that is in the Lemon. If you buy it in a pure form, it is a useful oil for various maintenance tasks for wooden objects.
The maker of three of my custom ukes recommended the use of real Lemon oil for the maintenance of fretboards. He knows what is on the fretboard and how to look after it and he will have to deal with any negative results.
As I posted above, the best source of information about the maintenance of your ukulele is the maker or manufacturer. If you have a custom uke, most makers will respond to a polite request about care and maintenance, even to the second or third owner. Maybe not immediately if they are busy, but eventually. If you own a production uke, look at the website. If you can't find the information, you are stuck with a thread like this and will see a variety of advice and you have to work out for yourself which advice to follow.