Transferring the celebration to a non-Lenten day is an option. We do it for St. George.
Depending on the date of Pascha, transfer it to a day after the Great Lent or before it. And it goes for any other celebration occuring in any fasting period (I mean especially the fasts last more than 1 day). It's really nice to have 2 great occassions.
Any two other things (their just my personal opinion, it's always good to ask your priest):
1. Try to accustom your children to the fasting period, and, generally, the whole family (that's in fact Home/Small/Local Church) should follow together (as the one community) the Church calendar. And it consists of both: feasts and fasts.
2. I treat "lenten" cake as deceiving God a bit. We fast not only from the certain products, but also things connected to them, including the taste and the atmosphere of celebration (that we link to cakes). And such attitude "Cake without dairy" reminds me Jewish practice regarding religious prohibitions and requisitions.