Is it worth changing career?

I am a 27 year old woman, I live with my partner and little boy who is nearly 3. I currently work as a Hairdresser 3 days a week ,but have been offered a job as a trainee dental nurse after applying out of interest. I have really started to dislike my job over the last few years. I love the people I work with but find the job stressful and I don't enjoy it anymore. I have been interested in becoming a dental nurse for some time but no dental practise has given me a chance due to no experience. The only problem is as I will be a trainee nurse I will be earning �3000 less a year doing the same hours as I do now, and also will no longer be getting tips. I will have to go back to college which i'm more than happy to do and the course is 2 years long.I would like more children in the future and do not want to leave it years and years. The main dilemma i'm in is that do I stay in a job I cannot progress any further in but can manage quite well financially and have more children whenever the time is right, or start a whole new which means going back to college and earning a lot less money but has the potential for me to go as far as I wish, so in the future I will be earning an excellent wage, but have to put having more children on hold. My partner and family are very supportive on either decision I make but I really can't decide and I'm running out of time. Other peoples opinons would be highly valued :)