Depends on the distance.
For example, Earth (mass 6x10^24 kg) has enough gravity to pull objects at about 10 m/s^2. To the 50kg girl, that is 10 times 50 = 500N.
Earth is 10^23 times heavier than the boy, so divide by 10^23 and you get 5x10^(-21)N at a distance of 6360km.
It depends on the distance too; the pull is inverse to the distance squared. Make the distance somewhat more reasonable, say, 6.36 km; that would be 5x10^(-15)N.
0.636m, and the formula will unfortunately break down, for the boy and the girl arent even approximately spherical; and at that close proximity, it will matter.
It would be 5x10^(-7)N according to the formula but thats only accurate to the order of magnitude; it could be half that force or maybe even less. It would be still quite accurate if they were not sitting, but curled up this time.
Hope that gives you an idea how small the forces are. Not the usual kind of attraction between boys and girls.