Hi J.! I have twins that are 5 1/2 and a 3 year old. I started putting my girls in their cribs when they were 3 months old which some might think is too little. It worked for me however, and they liked their cribs versus the bassinett in my room.
I let them cry for 10-15 minutes and then I would poke my head in and check up on them to make sure they were not crying from something other than not wanting to go to sleep right away. Sometimes I would sit on the floor next to the crib and sing softly to them or rub/pat their backs until they relaxed enough to fall asleep. Sometimes they just wanted to see me so I would sit on the floor and slowly move a little towards the door as they got sleepy until I made it out the door and they were gone! My twins always slept with soft music playing. I did children's music and classical. They also went to sleep at night with their little lamp on. Once they were about 2 yrs old, they started only wanting a small night light on. They cry if they don't have it on, to this day!
Also see if closing or opening the door to their room makes a difference. All of my kids wanted their doors closed and cried until I closed them. My co-worker however, has to have the door open to her daughter's room or she cries non stop. Routine makes a big, big difference. Find one and stick to it as much as possible for instance, naps (1-2 during day), bath before bed, read a story, bedtime 7/7:30, soft music playing, night light, door open/closed. Children love and need routine. It makes them feel safe and they know their tiny world is ok.
To this day, my children do not fight me when it is bed time (they even ask to go to bed!) which is 8/8:30. They don't fight me to take a nap and they love to read because we made it part of the routine when they were babies. They also love music. I have never had a problem keeping them out of my own bed either. They love their beds/rooms and they don't ask to sleep with my husband and I which makes everyone happy! :-)
I hope this helps you. It does get better as they get older and overcome fears, etc. Good luck!