When I was on my Aerodrome course, there was a woman on that course who had two children before she started.
I don't think NATS were too bothered about that and if anything, it helped her to get the posting she wanted once she'd left the college.
There was also another girl who got pregnant during another course I was on, and it gave her leverage to get the posting she wanted too.
Most of the people at the top of the tree in the college are now women and are probably more understanding than a fella would be.