I checked my young trees I kept in the basement this winter. Three of them have started leafing out and they are a little pale. I bought them up and put them in a sunny window. Before I leave them to long, do I need to aclimate them to the house temp? It went from probably high 40s to 70s.

Killed so many like that last year. Take them out of the sunny window right away!

They can dry out faster and the direct sunlight and heat may simply fry the new leaves. Put them in indirect sunlight instead, maybe across the room from the window but watch the moisture level because they will drink faster as the house is warmer. That doesn't mean water them more but rather be mindful of their needs and check on them more frequently. I had a propensity to water more (and drown and rot well rooted cuttings) while checking more but they should not be paired activities out of habit and the need to futz around. 

Are they in a humid environment now like a tupperware? If so maybe erect a bag over them for a week to help maintain some moisture and ease the transition.

These are not newly rooted cuttings. These are established trees in 1 gallon pots. They were dormant in the basement, bnow they are leafing out. I have never had any leaf out early like this.

Since the leaves are young and tender give the above a try. They should turn green pretty quickly with indirect light and safely.

Try this as a possible solution. In a couple of weeks move one of the trees that have been indirect sunlight closer to direct sunlight but not in it right away. If it fairs well after a few days bring a few more into its position. I would just not be in a hurry to get them into direct sunlight until you can see one can handle it well after some mild exposure and time to adapt.

I and may other I suspect also have staging areas around our homes, garages, family rooms, under trees where these young trees are designated to toughen up a little until the can play in the sun. 

It is supposed to be rainy and cloudy for the next few days. I don't have them where they will get hit with crazy sun and there is only one full tiny leaf anyway. The others are just buds breaking. i will kepe an eye on them.

If there are buds breaking get them in full sun.  Whatever they open to they'll adapt to.  If no sun get them into as much light as possible.  Water according to what the soil feels like.  Check the bottom holes.  As long as they're not sitting in water and not totally dry they'll be fine.

Great question.  A few minutes ago, I noticed my potted 1 year old tree has broken its bud shell with a tiny leaf about to emerge.  Mine is in the attached garage.  I'd like to hear more opinions on this matter myself.

In my windows I have a sheet of poly/plexy glass that looks like "Crackled glass"  ,
(used in suspended ceilings under fluorescent lights for light dispersion)
Comes in 4' X 2' sheets for about $7.00 a sheet at Lowes. Cut-able with hand shears.
Lets full sunlight in but, it breaks up sunlight like a myriad of tiny prisms so it doesn't burn your plants.
Works great as glass insulation, and for privacy too!

I have a two year old unknown variety(dark fig) that was in my tool shed a few weeks ago when we had 3 days of 9*F weather...it was frozen solid including the root ball...dragged it into my office where it is usually 65*F to thaw it out for a few weeks...now, believe it or not, it is in serious bud break with small leaves bursting out on all branches...so in an effort to slow it down a little I put it in my attached garage(around 45*F) and only bring it back in the office when we have a sudden temp drop(30*F) or less...I have no way to give it any sun light as the office and garage have no windows, and it is too cold and windy to put it outside...the garage has a 4' florescent shop light that I keep on...the office has 4 ceiling mounted florescent lights and two small T5 fixtures that are being used on cuttings...so at this time that is all the artificial sun that I can offer...keeping my fingers crossed that the tree will make it about 4 more weeks until April 1st., at which time it will be going outside

Well, they are back down I. The basement now! It didn't take one day for fungus nats to swarm out from those pots. I put them back in the basement and under a small grow light. Hopefully, the nats that got out don't take down my new cuttings.